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Professor John Edwin Field passed away on October 21st, 2020 at the age of 84. Professor Field was widely regarded as a leader in high-strain rate physics and explosives. During his career in the Physics and Chemistry of Solids (PCS) Group of the Cavendish Laboratory at Cambridge University, John made major contributions into our understanding of friction and erosion, brittle fracture, explosives, impact and high strain-rate effects in solids, impact in liquids, and shock physics. The contributions made by the PCS group are recognized globally and the impact of John’s work is a lasting addition to our knowledge of the dynamic effects in materials. John graduated 84 Ph.D. students and collaborated broadly in the field. Many who knew him attribute their success to the excellent grounding in research and teaching they received from John Field.

The response of Viton B, a fluorinated tripolymer, to one dimensional shock loading has been investigated using manganin stress gauges as the diagnostic. These have been mounted such that they are sensitive to both the longitudinal and lateral components of stress. In the case of the longitudinal gauges, mounting at multiple locations within the target assembly also allows measurement of shock and release velocities as well. Results show that in terms of shock velocity and stress and shear strength, results from Viton B lie a little higher than the corresponding results for polytetrafluoroethylene (PTFE), but more similar to those of polyvinylidene difluoride (PVDF). However, in terms of the release velocity, the behaviour of Viton B is more akin to PTFE. We believe that there are two competing mechanisms at play; an electrostatic repulsion between chains due to the presence of electronegative fluorine atoms that acts against interchain interactions (hence the low shock and high release velocities) and interchain entanglement (tacticity) due to the presence of trifluoromethyl side groups on one of the monomer sub units. This will result in a greater shock velocity and increase in shear strength behind the shock front (when compared to PTFE) as adjacent polymer chains physically interact via entanglement. This should reduce the release velocity for similar reasons; however the release behaviour of Viton B and PTFE is similar. We thus suggest that the electrostatic repulsion between chains may be acting over a longer length scale than interchain entanglement.

The limits of elastic behaviour change with the nature of the impulse applied to a target and the size of volume interrogated by a measurement, since it is the pre-existing defects sampled within its rise that determine the response observed. This review considers a range of solids of different material classes and tracks the development of the strength of the material during shock loading, from yield at the Hugoniot elastic limit, across the weak shock regime, to its transition to strong shock behaviour. It is shown that at this stress, the weak shock limit (WSL), the shear component of the applied stress exceeds the theoretical strength of the material. Beyond this threshold, there are a number of new responses that confirm a transition from an inhomogeneous to a homogeneous state. Further, whilst strength rises across the weak shock regime, it saturates at the WSL. For instance, failure in shocked glasses transitions from localised fracture initiated at target boundaries to a global failure at this threshold at the theoretical strength. Sapphire′s strength asymptotes to the theoretical strength of the strongest direction in its lattice. Finally, the fourth-power dependence of strain rate upon stress appears to be a consequence of the homogeneous flow in the strong shock regime. This review suggests that µ/2πis a good approximation for the unrelaxed theoretical strength of solids at increasing stresses beyond the WSL. The methodology unfolded here represents a new means to experimentally determine the ultimate shear strength of solids.

Polyvinylidene difluoride (PVDF) has found application as a piezoelectric stress gauge for the measurement of the shock response of materials. Therefore, it is perhaps surprising that little data concerning its bulk response to shock loading has reached the open literature. In this paper, we examine the behaviour of this polymer, both hydrostatically (equation of state; shock stress, shock velocity and particle velocity), and its deviatoric response (shear strength behind the shock front). Equation-of-state measurements show close agreement with existing data, but also a strong non-linearity in shock velocity at low particle velocities. The calculated hydrodynamic response also agrees well with existing pressure measurements, but is significantly lower than the measured shock stresses, suggesting that the shear strength of this material has a strong positive dependence on the applied shock pressure. Subsequent measurements of the lateral component of stress, which in combination with the known longitudinal stress has been used to calculate the shear strength, has confirmed this.

The shock induced mechanical response of two γ-titanium aluminides has been investigated using the technique of plate impact. It has been found that the HEL, spall strength and shear strengths are all dependent upon the initial microstructure, with the material possessed of the duplex microstructure being the stronger. This is in agreement with quasi-static measurements. Shear strength has been observed to increase rapidly with increasing longitudinal stress. more so than in Ti-6AI-4V. indicating that the high degree of work hardening is an important factor in determining the shear strength of metallic and intermetallic materials.

Il is a pressing objective to understand the mechanical behaviour of polymeric materiais at high strain rate for a range of industrial and defence applications. Some are used as the binder phase in plastic bonded explosives (PBXs) and propellants. Others are used either as components for structures or as the binder phase in various composite Systems. Such materials need to be understood so that their response may be understood and constitutive descriptions constructed. This work presents experimental data focused at the evaluation of the equation-of-statc (EOS) and strength behaviour of four selected polymers. The equation of state and the shear strength of each polymer were measured as a function of impact stress and this gives insight into the role of the microstructure and its relation to response.

Shock-loading of a material in contact with a high explosive (HE) experiences a “Taylor wave" (triangular wave) loading profile. Samples of 316L stainless steel were shock loaded to several peak pressures to examine the influence of square-topped and triangular (“Taylor-wave")-shaped pulse loading on spallation behavior. The 316L SS sample loaded to 6.6 GPa using a square-topped pulse with a pulse duration ouf 0.9 μsec displayed incipient spallation while the sample loaded to the identical peak shock pressure but with a triangularshaped loading pulse (which immediately unloads the sample after the peak Hugoniot stress is achieved) exhibited no damage. To achieve an approximately equivalent level of incipient spall using a triangular-shaped loading pulse, an ~ 2X increase in the peak Hugoniot stress was required. Detailed metallographic and microtextural analysis of the damage evolution in spalled 316L SS samples as a function of loading pulse shape and the peak Hugoniot stress is presented.

The shock response of four common semicrystalline thermoplastic polymers—polyethylene (PE), polyvinylchloride (PVC), polytetrafluoroethylene (PTFE) and polychlorotrifluoroethylene (PCTFE)—have been studied in terms of their Hugoniots, release velocities and shear strengths. Through the variations in behaviour caused by changes to the attached atoms to the carbon backbone, it has been possible to suggest that there are two main factors in play. The first is an electrostatic repulsion between adjacent polymer chains. Where this force is large, for example in PTFE with highly electronegative fluorine atoms, this results in this force dominating the shock response, with low shock velocities, high release velocities and little if no hardening behind the shock front. In contrast, in materials such as PE, this force is now weaker, due to the lower electronegativity of hydrogen, and hence this force is easier to overcome by the applied shock stress. Now the main factor affecting shock behaviour is controlled by the shape of the polymer chain allowing inter chain tangling (tacticity). This results in higher shock velocities, lower release speeds and significant hardening behind the shock front as the chains are forced together. This is prevalent in materials with a relatively open structure such as PE and is enhanced with the presence of large side groups or atoms off the main polymer chain.

Manganin stress gauges have been placed in samples of a γ-titanium aluminide alloy in such orientation that renders them sensitive to the lateral component of stress during one-dimensional shock loading. The impact stresses were in the range 1.8 to 6 GPa. The resultant stress histories show clear evidence of a transition from elastic to plastic behaviour, which, through the elastic relations correlates with the Hugoniot Elastic Limit of this material. In combination with the longitudinal stress data, it has been possible to use the lateral stresses from this series of experiments to calculate the shear strength during shock loading. The Hugoniot of the γ-titanium aluminide studied is seen to be significantly different than a standard α-β Ti-alloy such as Ti-6Al-4V. The results show this titanium aluminide alloy displays a significant degree of hardening with increasing shock stress.

The response of brittle materials to uniaxial compressive shock-loading has been the subject of much recent discussion. The physical interpretation of the yield point of brittle materials, the Hugoniot elastic limit (HEL), the rate-dependence of this threshold, and the effect of polycrystalline microstructure still remain to be comprehensively explained. Evidence of failure occurring in glasses behind a travelling boundary that follows a shock front has been accumulated and verified in several laboratories. Such a boundary has been called a failure wave. The variations in properties across this front include complete loss of tensile strength, partial loss of shear strength, reduction in acoustic impedance, lowered sound speed and opacity to light. Recently we have reported a similar behaviour in gabbro and the polycrystalline ceramics SiC, alumina and titanium diboride. It is the object of this work to present further observations of these phenomena and their relation to ballistic performance.

The subject area covered by this review is a large and important one and to do it full justice would require a larger format than is available here. However, an attempt is made to outline the history of some of the more important developments and to include most major techniques. Taylor impact, Hopkinson bar testing in its various forms and 1-D plate impact are all considered in some detail. High-speed photography, particularly when used in association with optical techniques, is a key area and recent advances are discussed.

Over the last ten years several observations have been made of compressive failure in glass by a so called fracture wave. A high-speed photographic study has been conducted in order to observe the propagation of fracture waves in glass. Streak and framing photography have been used to determine details of the wave speed and surface structure of fracture waves induced in glasses by planar impact. A 50 mm single stage gas gun was used to launch copper flyer plates at velocities of up to 1 km s-1. A computer controlled high-speed camera was used capable of exposure and interframe times from 50 ns upwards. Simultaneous measurements of the longitudinal stresses were made using manganin pressure gauges embedded in the samples. Results will be presented showing separation between the shock and fracture fronts suggesting that the failure mechanism is by compression rather than resulting from relief waves propagating from the free surfaces.

Plate impact experiments have been carried out on two aluminas of differing grain size using the Cambridge 50 mm gas gun. Tiles were constructed in thicknesses of 4,8 and 12 mm and were impacted by 3 mm thick copper projectiles fired at 550 m s-1. The longitudinal stress in the tiles was recorded using manganin stress gauges and a 1 GS s-1storage oscilloscope. Measurements were made of the elastic precursor of the deformation wave in each of these experiments. It was found that the elastic precursor varied significantly with thickness and that different behaviours were shown by the large and small grain size materials

The performance of armour materials depends upon the deformation mechanisms operating during the penetration process. The critical mechanisms determining the behaviour of armour ceramics have not been isolated using traditional ballistics. It has recently become possible to measure strength histories in materials under shock. The data gained for the failed strength of the armour are shown to relate directly to the penetration measured. Furthermore, it has been demonstrated in one-dimensional strain that the material can be loaded and recovered for post-mortem examination. Failure is by microfracture, which is a function of the defects and then cracking activated by plasticity mechanisms within the grains and failure at grain boundaries in the amorphous intergranular phase. Thus, it appears that the shock induced plastic yielding of grains at the impact face that determines the later time penetration through the tile.

Polyvinylidene difluoride (PVDF) has found application as a piezoelectric stress gauge for the measurement of the shock response of materials. Therefore, it is perhaps surprising that little data concerning its bulk response to shock loading has reached the open literature. In this paper, we examine the behaviour of this polymer, both hydrostatically (equation of state; shock stress, shock velocity and particle velocity), and its deviatoric response (shear strength behind the shock front). Equation-of-state measurements show close agreement with existing data, but also a strong non-linearity in shock velocity at low particle velocities. The calculated hydrodynamic response also agrees well with existing pressure measurements, but is significantly lower than the measured shock stresses, suggesting that the shear strength of this material has a strong positive dependence on the applied shock pressure. Subsequent measurements of the lateral component of stress, which in combination with the known longitudinal stress has been used to calculate the shear strength, has confirmed this.

ABSTRACTPrevention of sexually transmitted infections is a priority in developed and developing countries. One approach to prevention is the use of topical microbicides, and one promising approach is the use of dendrimers, highly branched macromolecules synthesized from a polyfunctional core. Three new dendrimer products developed to provide stable and cost-efficient microbicides were initially evaluated in vitro for anti-herpes simplex virus activity and then in vivo by using a mouse model of genital herpes. From these experiments one product, SPL7013, was chosen for further evaluation to define the dose and duration of protection. Unformulated SPL7013 provided significant protection from genital herpes disease and infection at concentrations as low as 1 mg/ml and for at least 1 h following topical (intravaginal) administration of 10 mg/ml. This compound was then formulated into three vehicles and further evaluated in mouse and guinea pig models of genital herpes infection. In the murine evaluations each of the formulations provided significant protection at concentrations of 10 and 50 mg/ml. Formulated compounds provided protection for at least 1 h at a concentration of 10 mg/ml. From these experiments formulation 2V was chosen for dose ranging experiments using the guinea pig model of genital herpes. The guinea pig evaluations suggested that doses of 30 to 50 mg/ml were required for optimal protection. From these studies a lead compound and formulation (2V of SPL7013) was chosen for ongoing evaluations in primate models of simian immunodeficiency virus and Chlamydia trachomatisinfection.

It is important to understand the response of polymers to rapid loading. They are used in a variety of applications in the automotive and aerospace industries in which they are designed to absorb impact. The response of elastomers has been little studied at high rate, and this work aims to address this deficiency. In particular, the Hugoniot of the material is investigated using plate–impact experiments, measuring the stress at varying positions to determine the shock– and the stress–particle velocity state. Secondly, the shear strength of polychloroprene is explored using embedded lateral stress gauges. From these measurements, the shear strength has been determined as a direct experimental variable, and its variation with shock stress deduced. The mechanical response of the material is assessed in relation to other polymers studied.

The mechanism for the failure of brittle materials during uniaxial compressive shockloading has been the subject of much discussion. In particular, the physical interpretation of the yield point, the Hugoniot elastic limit, remains poorly understood. It is additionally hypothesized that different materials display differing modes of deformation at the limit of elastic behaviour. Other work has shown that boron carbide (B4C) exhibits a type of behaviour in a different class to that of other brittle materials. In particular, other ceramics show smooth stress and particle velocity profiles at Lagrangian positions within the flow, while boron carbide shows jagged histories at such points, perhaps indicating that fragmentation at the sensor position is more extreme. To try and explain the origin of this behaviour, another part of the stress field has been probed. By using the longitudinal and now the lateral stress profiles, it is possible to elucidate how the strength of the material varies across the shock front. In other ceramics, failure has been seen to occur behind a travelling boundary that follows a shock front that has been called a failure wave, across which the strength of the material is dramatically reduced. In order to elucidate whether this failure process occurs, gauges were embedded to measure the lateral stress behind the shock front in B4C. As in other materials, the stress in B4C was seen to rise across a failure front. However, this phenomenon only occurred over certain stress ranges. More significantly, the failure penetrated further into the ceramic than has been seen in other materials. A mechanical interpretation is suggested to explain the observed behaviour. This paper shows that boron carbide exhibits a unique shock response. Although a polycrystalline ceramic, it shows a behaviour similar to an amorphous glass. It gives indications of the form of a comprehensive material description for brittle materials that will form the basis for future work.

The failure of brittle materials in uniaxial compressive shock loading has been the subject of extensive recent discussion. The physical interpretation of the yielding process in titanium diboride and its Hugoniot elastic limit remain poorly defined. Titanium diboride is known to exhibit an anomalous Hugoniot containing cusps at 4.5–7 and 13–17 GPa, according to the production route adopted for the material. These features are additionally observed on the free–surface wave profiles. Various experimental and microstructural variables have been investigated to find an explanation for these features. In other ceramics, failure has been seen to occur behind a travelling boundary that follows a shock front, called a failure wave, across which the strength of the material has been shown to dramatically decrease. In order to elucidate whether the cusps in titanium diboride are related to failure processes, gauges were embedded in order to measure the lateral stress behind the shock front. As in other materials, the stress in titanium diboride was seen to rise across a failure front. However, this process only occurred over certain stress ranges. A mechanical interpretation of the shock response of titanium diboride as a function of peak shock pressure is suggested relating to the cusps observed.

Shock wave profiles have been measured simultaneously using the velocity interferometry system for any reflector (VISAR) and embedded foil stress gauges. The gauge is backed using a transparent rear window made of polymethylmethacrylate, through which the laser beam entering the VISAR cavity is also shone. The technique is applied to grades of alumina of differing purity shocked just above the threshold normally taken to be the Hugoniot elastic limit (HEL). In the case of one of the aluminas, the result is analogous to metals with a small spall (dynamic tensile strength) signal recorded. In the case of the other materials, the signals show marked differences, indicating both the need for simultaneous measurement using a variety of sensors and the limitations of the present definitions for the mechanical thresholds in dynamic compression (HEL) and tension (spall strength).

ABSTRACTDendrimers are large highly branched macromolecules synthesized from a polyfunctional core. They have shown a variety of biological properties, including, in some instances, antiviral activity. In this study, five dendrimers were evaluated for in vitro activity against herpes simplex virus (HSV) types 1 and 2 by cytopathic effect (CPE) inhibition and plaque reduction (PR) assay in human foreskin fibroblast cells. All of the compounds were active against both virus types in the CPE inhibition assay, in which drug was added to the cells prior to the addition of virus. Antiviral activity was reduced or lost in the PR assays, in which the cells were incubated with the virus before the drug was added. The prophylactic efficacy suggested that the dendrimers might have potential as topical microbicides, products intended to be applied to the vaginal or rectal mucosa to protect against sexually transmitted infections. Three dendrimers were evaluated for this application against genital HSV infection in mice. Two of the compounds, BRI-2999 and BRI-6741, significantly reduced infection rates when 15 μl of a 100-mg/ml solution was administered immediately prior to intravaginal challenge, and the most effective compound, BRI-2999, provided significant protection even when applied 30 min before challenge. This is the first report of microbicidal activity by dendrimers in vivo.

Recent observations of the collapse of single bubbles or clouds of cavities trapped within stationary acoustic fields have shown the production of light and these phenomena have been dubbed single– or multiple–bubble sonoluminescence. The experimental observation of the variations in the bubble radius with time, with simultaneous measurement of the light emission from the bubble, shows short pulses of light correlated closely with the point of minimum radius of the bubble. Results will be presented showing experimental observations of light produced from shock–collapsed cavities. The role of shock waves generated within the bubble by the motion of the walls will be discussed with application to the shock–wave hypothesis proposed as one of the mechanisms responsible for sonoluminescence. The likely asymmetry of the process, as recently proposed, and the consequent presence of a high–velocity jet will also be discussed. The effect of such ‘hot’ cavities within an explosive matrix is investigated and results are presented. The collapse of a single bubble shows that light emission from the explosive matrix is due to reaction caused by hydrodynamic heating by jet impact, notdue to conduction from heated gas during compression. Similar results are seen in arrays of collapsing cavities. The effects of close, inert particles are discussed and an example is given.

There is considerable interest in the performance of materials during impact. The usual approach involves the application of an individual technique, such as flash X–ray. We present a new method using high–speed photography to image simultaneously the penetration behaviour and the in–plane strains at the rear surface, obtained using a find–grid technique. The approach is illustrated by analysis of the impact of a rod travelling at 540 m s−1against a polymethylmechacrylate (PMMA) block. Quantitative information is presented on the shapes and the volumes of fragmented material and the displacements of the rear surface from initial impact to full penetration. These data should stimulate mathematical modellers using hydrocode methods. The techniques have general applicability to any isotropic material.

Cavities are present in a wide range of energetic systems by design or mischance. In either case, the presence of a bubble sensitizes the explosive to ignition when it is collapsed by a shock pulse. In this case, the temperature within the cavity is high as well as the collapse being asymmetric. Many authors attribute ignition to the adiabatic heating of the trapped gas. In this work, cavities are created within an ammonium nitrate emulsion matrix. They are large enough to be visualized using conventional optics with a high-speed camera. These relatively large cavities collapse in such a way that the ignition event is controlled by the hydrodynamic pressures generated by the impact of a high–speed liquid jet. It is thought that other mechanisms may dominate at different length–scales.

We have recently demonstrated that glasses show damage after the arrival of a plane, compressive shock wave. The failure travels, in this case, at a uniform velocity, increasing at higher stresses. The purpose of this paper is to show that a range of polycrystalline aluminas also show failure in a similar manner to glasses. The difference is that the wave in aluminas is slowed and eventually stopped leaving a surface failed zone, whereas the process continues in glasses without reducing speed. These surface failure zones have a marked effect. One of the consequences is that the Hugoniot elastic limit for these materials may have to be taken at a higher point in the stress history than is conventional. A second is that speculation about decays with distance of elastic precursors may refer to the stress at which the failure zone is formed rather than to the stress at which yielding takes place.

Shock–wave profiles have been measured by many techniques probing the stress or particle velocity histories of shocked materials. Among the most commonly used methods are the velocity interferometry system for any reflector (VISAR) and embedded foil stress gauges. It is relatively unusual to employ both these techniques simultaneously in an experiment. The gauge is backed using a transparent rear window made of polymethylmethacrylate (PMMA) through which the VISAR is also shone. Examples are given of results from the two techniques for metal, ceramic and glass targets, and the direct comparison validates the accuracy of earlier gauge data. Finally, the results are used to construct the principal Hugoniot of the PMMA window material to high accuracy.

Shocked glasses suffer a particular failure mode in which they lose strength behind a propagating front that is known as a failure wave. The glass shows high strength, which reduces after some time to a lower value as the failure front passes. Such behaviour is investigated using plate–impact loading experiments over a range of stresses and three glass types. The longitudinal and lateral stresses are measured using embedded manganin stress gauges and the strength is calculated in the normal way. The glasses range from an open–structured, low–density material to a filled dense one. Even though the heaviest glass is over twice the density of the lightest, the measured strengths follow a universal curve for values ahead and behind the failure wave. The common silicate network is suggested as the explanation for this property.

ABSTRACTNeuropharmacologic agents able to disrupt normal virus-neuron interactions may provide an alternative strategy for the treatment of herpes simplex virus (HSV) infections. We have previously shown that prophylactic treatment with capsaicin, a natural compound that alters function in sensory neurons, can protect guinea pigs against cutaneous HSV disease, even though the compound has no direct antiviral activity. Here we have examined the ability of civamide, the cisisomer of capsaicin, to interfere with HSV disease. We show that, even when the onset of treatment was delayed until after intravaginal virus challenge, primary genital skin disease severity was significantly reduced. In addition, animals treated during primary infection subsequently experienced a long-lasting reduction in recurrent disease. Civamide treatment during latent infection also significantly reduced recurrent disease, although for a shorter period. Further a single weekly treatment with civamide during latent infection was sufficient to reduce recurrent disease, indicating that an infrequent suppressive maintenance therapy might be possible.

An accurate model of the pressure-flow relationship of a stenosis is necessary for the correct interpretation of haemodynamic measurements. Modelled femoral artery stenoses were tested in vitroand the pressure drop: flow ratio (resistance) was most accurately represented by a fixed component (Rf) combined with a variable component (Rv) that increased linearly with flow (Q) such that Rv= SvQ. For stenoses of 68–94 per cent area, Rfincreased from 3·2 to 77·7 milliperipheral resistance units (mPRU), while Svincreased from 0·009 to 0·578 mPRU ml−1min and Rvwas dominant for physiological flow rates. It was concluded that the approximation of a significant stenosis to a fixed resistance is incorrect.

A series of experimental demonstrations of plasma injection into a burning propellant interface is presented. The propellant is a nitro‐guanidine based material in the form of a right cylinder with a bore along its central axis. It is ignited by a hot‐wire system and, when a pre‐set pressure is achieved, a second wire is exploded using a high‐voltage capacitor discharge circuit. The second wire forms a plasma, precisely at, or well away from the burning interface. Comparing the pressure histories from these different geometries allows the effect of increased burning rate to be separated from Joule heating of the product gases. Analysis of these histories shows a pressure increase over that caused by Joule heating of the products.

Varicella-zoster virus (VZV) is an attractive candidate for a live-virus vector for the delivery of foreign antigens. The Oka vaccine strain of VZV is safe and effective in humans, and recombinant Oka VZV (ROka) can be generated by transfecting cells with a set of overlapping cosmid DNAs. By this method, the herpes simplex virus type 2 (HSV-2) glycoprotein D (gD2) gene was inserted into an intergenic site in the unique short region of the Oka VZV genome. Expression of gD2 in cells infected with the recombinant Oka strain VZV (ROka-gD2) was confirmed by antibody staining of fixed cells and by immunoblot analysis. Immune electron microscopy demonstrated the presence of gD2 in the envelope of ROka-gD2 virions. The ability of ROka-gD2 to protect guinea pigs against HSV-2 challenge was assessed by inoculating animals with three doses of uninfected human fibroblasts, fibroblasts infected with ROka VZV, or fibroblasts infected with ROka-gD2. Neutralizing antibodies specific for HSV-2 developed in animals immunized with ROka-gD2. Forty days after the third inoculation, animals were challenged intravaginally with HSV-2. Inoculation of guinea pigs with ROka-gD2 significantly reduced the severity of primary HSV-2 infection (P < 0.001). These experiments demonstrate that the Oka strain of VZV can be used as a live virus vector to protect animals from disease with a heterologous virus.

Experiments were conducted to investigate the mechanisms of damage to brittle materials by liquid–jet impact as seen in cavitation or simulated rain erosion. In this work, a liquid–jet of 3 mm in diameter and speed ca. 600 m s-1, produced using the single–impact jet apparatus (SIJA), was impacted on a polymethylmethacrylate (PMMA) target, chosen as a representative brittle solid. Damage was produced by the liquid jet both near the surface of, and within the bulk of the target. These failure phenomena, which proceeded in several stages, were observed in detail by means of a high–speed camera and with the aid of schlieren visualization techniques. The damage introduced resulted from the interactions of stress waves (compressive, tensile and shear) within the target. A surface ring crack was produced behind a propagating release wave. A central crack along the axis of the jet was also produced by interaction of these waves and, in the case of targets of finite thickness, spall damage was observed at the rear surface. A further crack was opened by the interaction of a shear wave with a reflected release. All the failure mechanisms resulted from wave interactions induced in the target and occurred within a few microseconds of impact.

The role of putative promoter or activator sequences downstream of the herpes simplex virus type 2 latency-associated transcript (LAT) promoter and upstream of the LAT intron was investigated in vivo by constructing and evaluating mutant viruses with deletions in this region. The deletion of LAT promoter sequences upstream of the primary LAT transcript reduced levels of LAT expression during productive infections, compared with the LAT expression level of wild-type virus, and abolished LAT expression during latency. The deletion of the putative downstream regulatory elements reduced but did not eliminate LAT expression during productive and latent infections. The deletion of both regions almost completely eliminated acute LAT transcription, although additional acute LAT-region transcription directed by sequences upstream of either region was detected by reverse transcriptase PCR. The deletion of the downstream elements did not influence the ability of the virus to reactivate from latently infected guinea pigs relative to the ability of the wild-type virus to reactivate; thus, decreased LAT expression did not affect the frequency of recurrence. The deletion of both regions did not affect the ability of the virus to establish latency. We conclude that downstream regulatory elements are necessary for maximal acute LAT expression but do not constitute an independent promoter during latency and do not play an obvious role in the establishment of our reactivation from latency.

Herpes simplex virus (HSV)-coded thymidine kinase (TK) is important in efficient reactivation of latent infection. These studies were designed to investigate whether treatment of latently infected animals with a TK inhibitor altered the natural history of recurrent HSV disease. 9-([(Z)-2-(hydroxymethyl)cyclohexyl]methyl) guanine (L-653,180) is a potent and selective nonsubstrate inhibitor of HSV TK which can suppress or delay reactivation of HSV-1 from latently infected cells in vitro without affecting viral replication. In an initial study, six female Hartley guinea pigs were treated with L-653,180 in their diet (25 mg/30 g of food) and water (300 mg/liter) for 7 days. Blood, urine, kidney, liver, spinal cord, and cerebral cortex specimens were collected. L-653,180 was detected in all specimens at concentrations which, although low, were higher than the in vitro 50% inhibitory concentration of the drug against HSV TK. In the second study, 20 female Hartley guinea pigs were randomized into two groups following recovery from primary genital HSV-2 infection. One group received L-653,180 in diet and water for 4 weeks beginning 21 days postinoculation. Animals were examined daily for recurrent lesions for 10 weeks. Treated animals experienced fewer recurrences during the treatment period but the results were not significantly different from results with controls. During the first 2-week posttreatment period, L-653,180-treated animals had significantly fewer recurrences than control animals (P = 0.02). Over the entire 10-week observation period, treated animals experienced fewer recurrences (P = 0.06). These results suggest that inhibitors of viral TK may be useful in limiting reactivation of latent virus and thus recurrent infections. In these experiments, the amount of drug that could be administered to the animals was limited by its poor solubility. Further studies with more potent and soluble inhibitors of HSV TK appear to be warranted.

Spinal loading during weightlifting results in a loss of stature which has been attributed to a decrease in height of the intervertebral discs--so-called 'spinal shrinkage'. Belts are often used during the lifting of heavy weights, purportedly to support, stabilize and thereby attenuate the load on the spine. The purpose of this study was to examine the effects of a standard weightlifting belt in attenuating spinal shrinkage. Eight male subjects with a mean age of 24.8 years performed two sequences of circuit weight-training, one without a belt and on a separate occasion with a belt. The circuit training regimen consisted of six common weight-training exercises. These were performed in three sets of ten with a change of exercise after each set of ten repetitions. A stadiometer sensitive to within 0.01 mm was used to record alterations in stature. Measurements of stature were taken before and after completion of the circuit. The absolute visual analogue scale (AVAS) was used to measure the discomfort and pain intensity resulting from each of the two conditions. The circuit weight-training caused stature losses of 3.59mm without the belt and 2.87 mm with the belt (P greater than 0.05). The subjects complained of significantly less discomfort when the belt was worn (P less than 0.05). The degree of shrinkage was significantly correlated (r = 0.752, P less than 0.05) with perceived discomfort but only when the belt was not worn. These results suggest the potential benefits of wearing a weightlifting belt and support the hypothesis that the belt can help in stabilizing the trunk.

Juvenile scallops (<2 mm shell height) of three species (Placopecten magellanicus, Patinopecten yessoensis, Argopecten irradians) were fed mixed, unialgal cultures. Scallops were fed a total of six algal clones simultaneously and clearance rates were monitored using flow cytometric techniques. In another experiment, scallops were presented with natural assemblages of particulate matter as a food source. Data are presented on differences in clearance rates for the individual algal species as well as size-related differences of algal clones, and uptake of chlorophyll vs. non-chlorophyll cells, both within and between scallop species. Significant differences in clearance rates of individual algal species have been found within and between scallop species. Particle selection does not appear to be based upon size alone and is apparently based on other characteristics of the algae as well. The results demonstrate pre-ingestive sorting.

The latency-associated transcript (LAT) is the only herpes simplex virus (HSV) gene product detectable in latently infected humans and animals. In this report, we show that a 624-bp deletion in the promoter of the HSV-2 LAT had no discernable effect on viral growth in tissue culture or in acute genital infection of guinea pigs, but impaired LAT accumulation and led to a marked decrease in spontaneous genital recurrences when compared with the behavior of wild-type and rescuant strains. Differences in the ability of the mutant to replicate, or in how readily it established or maintained latency did not account for this finding. Thus, HSV LAT expression facilitates the spontaneous reactivation of latent virus.

The start sites for transcription and translation of a Bacillus subtilis spore coat protein gene, cotT, were determined. The CotT protein was synthesized as a 10.1-kDa precursor which was processed to a coat polypeptide of 7.8 kDa. Insertional inactivation of the cotT gene resulted in spores with an altered appearance of the inner coat layers and slow germination in response to a germination solution containing fructose, glucose, and asparagine. Rates of germination in L-alanine and in Penassay broth were the same as that of the wild type. A strain containing the cotT gene on a low-copy-number plasmid produced spores with an excess of CotT precursor and a thickening of the striated inner coat. These spores responded poorly to all of the germinants mentioned above. A site-directed mutation of the codon at the processing site of CotT resulted in the accumulation of the precursor in sporulating cells and on the spores, but there was no effect on the germination rates or solvent resistance of these spores. Both the lack and the overproduction of CotT led to subtle alterations in the structure of the inner spore coat and in the capacity of spores to respond to particular germinants.

After replication at sites of initial inoculation, herpes simplex virus type 1 and 2 (HSV-1 and HSV-2) establish lifelong latent infections of the sensory and autonomic neurons of the ganglia serving those sites. Periodically, the virus reactivates from these neurons, and travels centripetally along the neuronal axon to cause recurrent epithelial infection. The major clinically observed difference between infections with herpes simplex virus type 1 and type 2 is the anatomic site specificity of recurrence. HSV-1 reactivates most efficiently and frequently from trigeminal ganglia, causing recurrent ocular and oral-facial lesions, while HSV-2 reactivates primarily from sacral ganglia causing recurrent genital lesions. An intertypic recombinant virus was constructed and evaluated in animal models of recurrent ocular and genital herpes. Substitution of a 2.8-kbp region from the HSV-1 latency-associated transcript (LAT) for native HSV-2 sequences caused HSV-2 to reactivate with an HSV-1 phenotype in both animal models. The HSV-2 phenotype was restored by replacing the mutated sequences with wild-type HSV-2 LAT-region sequences. These sequences or their products must act specifically in the cellular environments of trigeminal and sacral neurons to promote the reactivation patterns characteristic of each virus.

Rate constants k are measured for the reaction of 27 phenols such as (I) and 8 further nucleophiles such as acetate, CF3‐CH(OH)‐CF3, CF3‐CH2‐OH with phosphinate (II) and of the phenols (V) with substituted phosphinates of type (VI).