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No reliable experimental data exist for the partial and total electron ionization cross sections for DNA bases, which are very crucial for modeling radiation damage in genetic material of living cell. We have measured a complete set of absolute partial electron ionization cross sections up to 500 eV for DNA bases for the first time by using the relative flow technique. These partial cross sections are summed to obtain total ion cross sections for all the four bases and are compared with the existing theoretical calculations and the only set of measured absolute cross sections. Our measurements clearly resolve the existing discrepancy between the theoretical and experimental results, thereby providing for the first time reliable numbers for partial and total ion cross sections for these molecules. The results on fragmentation analysis of adenine supports the theory of its formation in space. [ABSTRACT FROM AUTHOR]

We present a compact cold-wall oven that is simple to build and align for loading miniature ion traps with calcium ions. The cold-wall oven, which is a metal-loaded capillary heated only through a portion of its length by the passage of a current, is described and characterized. An atomic beam with a low divergence of 14 mrad is produced. We perform Doppler-sensitive, resonant fluorescence measurements on the atomic beam to characterize the oven's performance. The emission of atoms from the oven is seen within ∼70 s after turning on the oven at an electric power consumption of < 10 W. The flow rate is measured to be 1.5 ± 0.2 × 109 atoms s−1 at a temperature of 702 ± 7 K. The entire oven assembly is mounted on a CF16 feedthrough. This design can be extended to other species for producing a collimated atomic beam. [ABSTRACT FROM AUTHOR]

Absolute partial and total electron ionization cross sections for uracil in the gas phase as a function of energy up to 500 eV are measured using the well-known relative flow technique (RFT). These measurements have significant consequences for the study of radiation damage, tests of several theoretical models and application of the RFT for molecules existing in solid form at room temperature. Also presented are the thresholds for the formation of various fragment ions from uracil and the comparison of total ionization cross section with the existing results. [ABSTRACT FROM AUTHOR]

Abstract: The velocity slice imaging technique is used to obtain the kinetic energy and angular distributions of H− and ions formed by dissociative electron attachment (DEA) to methane. The data show two distinct anion states in the broad peak between 8 and 12eV with the lower energy one undergoing two-body fragmentation, while the higher energy one undergoing a three-body fragmentation. The dissociation process is seen to be influenced by the Jahn–Teller effect similar to that seen in methane cation and its neutral counterpart. [Copyright &y& Elsevier]

Adjuvant induced arthritis is a chronic crippling, skeleton-muscular disorder having nearest approximation to human rheumatoid arthritis for which there is currently no medicine available effecting a permanent cure. Even modern drugs used for the amelioration of the symptoms, offer only temporary relief and also produce severe side effects. In the indigenous system of medicine, wood of Premna serratifolia Linn., is reported to be useful in the treatment of arthritis. It is a large shrub, distributed throughout Asia, used against a wide variety of diseases. However, no systematic study has been reported regarding its anti-arthritic activity. This work was aimed at the scientific validation of the ethno-pharmacological claim about its anti-arthritic property. In the present study, anti-arthritic activity of ethanol extract of Premna serratifolia Linn., wood is done by Freund's adjuvant induced arthritis model. Loss in body weight during arthritis condition was corrected on treatment with ethanol extract and standard drug, indomethacin. Biochemical parameters such as hemoglobin content, total WBC, RBC, erythrocyte and sedimentation rate were also estimated. The ethanol extract at the dose of 300 mg/kg body weight inhibited the rat paw edema by 68.32% which is comparable with standard drug indomethacin 74.87% inhibition of rat paw edema after 21 days. The results of the current investigation concluded, ethanol extract of Premna serratifolia Linn., wood possess a significant anti-arthritic activity against adjuvant induced arthritis and justifying its therapeutic role in arthritic condition. The observed antiarthritic activity may be due to the presence of phytoconstituents such as irridiod glycosides, alkaloids, phenolic compounds and flavonoids. [ABSTRACT FROM AUTHOR]

Abstract: Dissociative electron attachment to SO2, NO2, NF3 and H2O2 is studied in terms of the kinetic energies of the dominant fragment ions. The O− data from SO2 show that the two major resonances at 4.6 and 7.2eV respectively have the same dissociation limit. Similarly, the resonances at 1.8 and 3.5eV in the O− channel in NO2 appear to have same dissociation limit of NO (X 2Π)+O−, while the resonance at 8.5eV appears to dissociate to give NO (a 4Πi) along with O−. We find considerable internal excitation of the neutral fragments in all these cases along with that of NF3, whereas the negative ion resonance in H2O2 appears to fragment almost like a diatomic system with very little internal excitation of the OH and OH− fragments. [Copyright &y& Elsevier]

Dissociative electron attachment (DEA) to hydrogen peroxide (H2O2) is studied by two independent electron beam experiments using mass spectrometric detection of the product ions. The fragments OH− and O− are observed from a prominent low energy resonance peaking near 0.4 eV. The partial absolute DEA cross-sections are 6.8×10−17 and 1.7×10−17 cm2 for the OH− and the O− channels, respectively. These numbers are several orders of magnitude higher than for the corresponding DEA processes in simple OH containing organic compounds. These numbers are also important from the point of view of radiation damage in biological tissues. [Copyright &y& Elsevier]

Negative ion resonance states of ammonia are accessed upon capture of electrons with energy 5.5 eV and 10.5 eV, respectively. These resonance states dissociate to produce H- and NH2- fragment anions via different fragmentation channels. Using the velocity slice imaging technique, we measured the angular and kinetic energy distribution of the fragment H- and NH2- anions with full 0-2π angular coverage across the two resonances. The scattered H- ions at both resonances show variation in their angular distribution as a function of the kinetic energy indicating geometric rearrangement of NH3-* ion due to internal excitations and differ from the equilibrium geometry of the neutral molecule. The second resonance at 10.5 eV shows strong forward-backward asymmetry in the scattering of H- and NH2- fragment ions. Based on the angular distributions of the H- ions, the symmetry of the resonances at 5.5 eV and 10 .5 eV are determined to be A1 and E, respectively, within C3v geometry. [ABSTRACT FROM AUTHOR]

The role of a capillary array as a molecular beam source for use in recoil ion momentum spectrometry in ion-atom collisions is investigated. Numerical simulations show that by using a capillary array it is possible to obtain a half-width of 1 meV at room temperature, while the sensitivity could be in the range as low as 100 µeV. Preliminary measurements with electron impact ionisation showed the effectiveness of this technique by providing an energy resolution of about 2 meV at room temperature, which is superior to the resolution reported using a gas cell cooled to 30° K. [ABSTRACT FROM AUTHOR]

Dissociative electron attachment (DEA) to formic acid is investigated using velocity slice imaging of H− ions. From the momentum distributions, we infer that the broad peak observed in absolute cross section of H− between 6 and 12 eV has contribution from three resonances. The resonance below 7 eV shows angular distribution fairly close to that seen from the B1 resonance in water and the first peak of the two peaks from the hydroxyl site of acetic acid. The resonance observed around 9 eV appears to have definite contribution from the C-site of the molecule, as identified from the momentum distribution and similarity with other organic molecules including methane. The analysis of the kinetic energy distribution shows that the two resonances below 8 eV are dominated by the contribution from hydroxyl site of the molecule. The results indicate that formic acid tends to behave like other small carboxylic acids and alcohols and displays functional group dependence and corresponding site specificity in the DEA process, to a large extent. [ABSTRACT FROM AUTHOR]

In light of its substantially more environmentally friendly nature, CF3I is currently being considered as a replacement for the highly potent global-warming gas CF4, which is used extensively in plasma processing. In this context, we have studied the electron-driven dissociation of CF3I to form CF3− and I, and we compare this process to the corresponding photolysis channel. By using the velocity slice imaging (VSI) technique we can visualize the complete dynamics of this process and show that electron-driven dissociation proceeds from the same initial parent state as the corresponding photolysis process. However, in contrast to photolysis, which leads nearly exclusively to the 2P1/2 excited state of iodine, electron-induced dissociation leads predominantly to the 2P3/2 ground state. We believe that the changed spin state of the negative ion allows an adiabatic dissociation through a conical intersection, whereas this path is efficiently repressed by a required spin flip in the photolysis process. [ABSTRACT FROM AUTHOR]

In light of its substantially more environmentally friendly nature, CF3I is currently being considered as a replacement for the highly potent global-warming gas CF4, which is used extensively in plasma processing. In this context, we have studied the electron-driven dissociation of CF3I to form CF3− and I, and we compare this process to the corresponding photolysis channel. By using the velocity slice imaging (VSI) technique we can visualize the complete dynamics of this process and show that electron-driven dissociation proceeds from the same initial parent state as the corresponding photolysis process. However, in contrast to photolysis, which leads nearly exclusively to the 2P1/2 excited state of iodine, electron-induced dissociation leads predominantly to the 2P3/2 ground state. We believe that the changed spin state of the negative ion allows an adiabatic dissociation through a conical intersection, whereas this path is efficiently repressed by a required spin flip in the photolysis process. [ABSTRACT FROM AUTHOR]

Highlights: [•] In DEA and as well in DD to ethylene H−, C−, CH−, CH2 −, C2 −, C2H−, C2H2 − and C2H3 − anions are observed. [•] Newly observed anions for ethylene are: C− and C2H2 −. [•] The present calculations of thermochemical thresholds indicate that for several resonances formation of stable neutral molecules from released fragments occurs which lowers the threshold of the DEA reaction. [Copyright &y& Elsevier]

We report the molecular dynamics of dissociative electron attachment to sulfur dioxide (SO2) by measuring the momentum distribution of fragment anions using the velocity slice imaging technique in the electron energy range of 2-10 eV. The S- channel results from symmetric dissociation which exhibits competition between the stretch mode and bending mode of vibration in the excited parent anion. The asymmetric dissociation of parent anions leads to the production of O- and SO- channels where the corresponding neutral fragments are formed in their ground as well as excited electronic states. We also identify that internal excitation of SO- is responsible for its low yield at higher electron energies. [ABSTRACT FROM AUTHOR]

The dynamics of the formation and decay of negative ion resonance of A symmetry at 8.5 eV electron energy in the dissociative electron attachment (DEA) process in HO and DO are investigated using the velocity slice imaging technique. While the highest energy hydride ions formed by DEA show angular distributions characteristic to the A symmetry, those formed with low-kinetic energy show considerably different angular distributions indicating changes in the orientation of the dissociating bond due to bending mode vibrations. Our observations are quite different from the recently reported measurements, but consistent with the fully quantum calculations. [Figure not available: see fulltext.] [ABSTRACT FROM AUTHOR]

Abstract: This paper describes the attitude control schemes for the various phases such as acquisition, on-orbit, orbit maneuver, de-boost maneuvers and coast phases of the India''s first recovery mission Space Capsule Recovery Experiment-I (SRE-1). During the on-orbit phase, the SRE was configured to point the negative roll axis to Sun. The attitude referencing of SRE-1 was based on dry tuned gyros with updates from the attitude determined using on-board Sun sensors and magnetometer. For attitude acquisition, attitude maneuvers and for providing the velocity corrections for de-orbiting operations; a set of eight thrusters grouped in functionally redundant blocks were used. The control scheme with thrusters was based on proportional derivative controller with a modulator. In order to ensure micro-gravity environment during the on-orbit payload operations a linear quadratic regulator (LQR) based control scheme was designed to drive an orthogonal configuration of magnetic torquers which in turn produced three-axis control torque with the interaction of Earth''s magnetic field. Proportional derivative control scheme with modulator was designed to track the steering commands during the velocity reduction as well as during the coasting phase of the de-orbiting operations. A novel thruster failure detection, isolation and reconfiguration scheme implemented on-board for the de-orbiting phase is also discussed in this paper. [Copyright &y& Elsevier]

Abstract: The development of an experiment for velocity map imaging (VMI) of fragment ions arising from electron–molecule collisions is discussed. The angular distribution of O− from the dissociative attachment and dipolar dissociation of O2 is measured and compared with the existing data. The details of the technique and its importance to electron–molecule collisions are discussed. [Copyright &y& Elsevier]

Low energy electron attachment to the fullerene molecule (C60) and its temperature dependence are studied in a crossed electron beam–molecular beam experiment. We observe the strongest relative signal of C60 anion near 0 eV electron energy with respect to higher energy resonant peaks confirming the contribution of s-wave capture to the electron attachment process and hence the absence of threshold behavior or activation barrier near zero electron energy. While we find no temperature dependence for the cross-section near zero energy, we observe a reduction in the cross-sections at higher electron energies as the temperature is increased, indicating a decrease in lifetime of the resonances at higher energies with increase in temperature. [ABSTRACT FROM AUTHOR]

A velocity slice imaging method is developed for measuring the angular distribution of fragment negative ions arising from dissociative electron attachment (DEA) to molecules. A low energy pulsed electron gun, a pulsed field ion extraction, and a two-dimensional position sensitive detector consisting of microchannel plates and a wedge-and-strip anode are used for this purpose. Detection and storage of each ion separately for its position and flight time allows analysis of the data offline for any given time slice, without resorting to pulsing the detector bias. The performance of the system is evaluated by measuring the angular distribution of O- from O2 and comparing it with existing data obtained using conventional technique. The capability of this technique in obtaining forward and backward angular distribution data is shown to have helped in resolving one of the existing problems in the electron scattering on O2. [ABSTRACT FROM AUTHOR]

A PC based data acquisition cum control system has been developed using a general purpose interface bus (GPIB/IEEE-488/IEC-625) plug in card and GPIB interfaceable NIM electronics for use in experiments on absorption spectroscopy studies of molecules using laser-induced fluorescence (LIF), resonance multiphoton ionization (REMPI), electron impact ionization and dissociative attachment from the ground state as well as from excited states, to name a few examples. Unlike commercially available multichannel scalers, this system can handle several parameters as the acquisition parameter (e.g., dye laser) is scanned over the desired wavelength in preselected segments saving precious data acquisition time. This system has been tested on laser excited dissociative electron attachment experiments. [ABSTRACT FROM AUTHOR]

Pulmonary alveolar proteinosis (PAP) is a rare disease, characterized by alveolar accumulation of surfactant composed of proteins and lipids due to defective surfactant clearance by alveolar macrophages. Mainstay of treatment is whole lung lavage, which requires general anesthesia. Herein, we report a case of primary PAP, successfully treated with serial bronchoscopic lung lavages under local anesthesia. [ABSTRACT FROM AUTHOR]

Dissociative electron attachment (DEA) to acetone is studied in terms of the absolute cross section for various fragment channels in the electron energy range of 0-20 eV. H- is found to be the most dominant fragment followed by O- and OH- with only one resonance peak between 8 and 9 eV. The DEA dynamics is studied by measuring the angular distribution and kinetic energy distribution of fragment anions using Velocity Slice Imaging technique. The kinetic energy and angular distribution of H- and O- fragments suggest a many body break-up for the lone resonance observed. The ab initio calculations show that electron is captured in the multi-centered anti-bonding molecular orbital which would lead to a many body break-up of the resonance. [ABSTRACT FROM AUTHOR]

Dissociative electron attachment (DEA) cross sections for simple organic molecules, namely, acetic acid, propanoic acid, methanol, ethanol, and n-propyl amine are measured in a crossed beam experiment. We find that the H- ion formation is the dominant channel of DEA for these molecules and takes place at relatively higher energies (>4 eV) through the core excited resonances. Comparison of the cross sections of the H- channel from these molecules with those from NH3, H2O, and CH4 shows the presence of functional group dependence in the DEA process. We analyze this new phenomenon in the context of the results reported on other organic molecules. This discovery of functional group dependence has important implications such as control in electron induced chemistry and understanding radiation induced damage in biological systems. [ABSTRACT FROM AUTHOR]

Following the recent report of the first identification of methyl acetate (CH3COOCH3) in the interstellar medium (ISM), we have carried out vacuum ultraviolet (VUV) and infrared (IR) spectroscopy studies on methyl acetate from 10 K until sublimation in an ultrahigh vacuum chamber simulating astrochemical conditions. We present the first VUV and IR spectra of methyl acetate relevant to ISM conditions. Spectral signatures clearly showed molecular reorientation to have started in the ice by annealing the amorphous ice formed at 10 K. An irreversible phase change from amorphous to crystalline methyl acetate ice was found to occur between 110 K and 120 K. [ABSTRACT FROM AUTHOR]

Exploiting the technique of velocity slice imaging, we have performed a detailed study of reactive electron scattering with CF4. We have measured the electron impact energy dependence of both the angular and kinetic energy distributions of the channels yielding F- and CF3- anions. These data provide an unprecedented insight into the quantum superposition of the target state and product channels, respectively, of Td and C3v symmetry, and shed new light on the dissociation dynamics. [ABSTRACT FROM AUTHOR]

Tremendous strides have been made in charged-particle acceleration using intense, ultrashort laser pulses. Accelerating neutral atoms is an important complementary technology because such particles are unaffected by electric and magnetic fields and can thus penetrate deeper into a target than ions. However, compact laser-based accelerators for neutral atoms are limited at best to millielectronvolt energies. Here, we report the generation of megaelectronvolt-energy argon atoms from an optical-field-ionized dense nanocluster ensemble. Measurements reveal that nearly every laser-accelerated ion is converted to an energetic neutral atom as a result of highly efficient electron transfer from Rydberg excited clusters, within a sheath around the laser focus. This process, although optimal in nanoclusters, is generic and adaptable to most laser-produced plasmas. Such compact laser-driven energetic neutral atom sources could have applications in fast atom lithography for surface science and tokamak diagnostics in plasma technology. [ABSTRACT FROM AUTHOR]

Abstract: Dissociative electron attachment (DEA) cross sections for NH3 and CH4 are measured in a crossed beam apparatus with special care to eliminate discrimination due to kinetic energy and angular distribution of the fragment ions. The cross sections are put on absolute scale using the relative flow technique. The absolute cross sections for the formation of H− and NH2 − from ammonia and H− and CH2 − from methane are compared with available data from literature. It is seen that the present results are considerably different from what has been reported before. We also compare the cross sections of the H− channel from these molecules along with that from H2O to those from organic molecules containing alkyl, amino and hydroxyl groups to examine the extent to which the recently observed functional group dependence in the DEA contributes. [Copyright &y& Elsevier]

D-Galactosamine (GalN)-induced liver injury is associated with reactive oxygen species and oxidative stress. In the present study, we evaluated the effect of alpha lipoic acid (ALA) supplementation on acute GalN-induced oxidative liver injury. Hepatotoxicity induced by single intraperitoneal injection of GalN (500 mg/kg body wt) was evident from increase in lipid peroxidation and serum marker enzymes (asparate transaminase, alanine transaminase, alkaline phosphatase, and lactate dehydrogenase). The decreased activities of enzymic antioxidants (superoxide dismutase, catalase, glutathione peroxidase, and glutathione reductase) as well as glutathione levels were the salient features observed in GalN-induced hepatotoxicity. Pretreatment with ALA (50 mg/kg body weight for 7 days) significantly precluded these changes and prevents the hepatic injury. Hence, this study clearly exemplified that ALA might be a suitable candidate against GalN-induced cellular abnormalities. [ABSTRACT FROM AUTHOR]

Abstract: Dissociative electron attachment to formic acid (HCOOH) is studied in a crossed beams experiment using mass spectrometric detection of the product ions in the electron energy range 0–15eV, including the measurement of absolute cross-sections. Unlike the previous reports, we observe the formation of H− from this molecule, in addition to the fragment negative ions namely O−/OH− and HCOO−, which were observed earlier. The absolute cross-sections indicate that H− formation is one of the important DEA channels in this molecule. [Copyright &y& Elsevier]