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The interactions between thermal phonons and defects are conventionally described as scattering processes, an idea proposed almost a century ago. In this contribution, ab-initio molecular-dynamics simulations provide atomic-level insight into the nature of these interactions. The defect is the Si|X interface in a nanowire containing a δ-layer (X is C or Ge). The phonon-defect interactions are temperature dependent and involve the trapping of phonons for meaningful lengths of time in defect-related, localized, vibrational modes. No phonon scattering occurs and the momentum of the phonons released by the defect is unrelated to the momentum of the phonons that generated the excitation. The results are extended to the interactions involving only bulk phonons and to phonon-defect interactions at high temperatures. These do resemble scattering since phonon trapping occurs for a length of time short enough for the momentum of the incoming phonon to be conserved.

The phase stability and site occupancy of bcc (body centered cubic) Nb(5)Al and slightly rearranged atomic structures have been examined by means of first-principles calculations. In order to use first-principles methods, a periodic cell is required and we used ordered Nb(5)Al compounds as a tractable example of a low Al concentration Nb(1 - x)Al(x) alloy (in this case, for about 17 at.% Al). The instability against an ω-structure atomic displacement was also studied, since this structure is detrimental to ductility. Mulliken population analysis was used to provide an understanding of the hybridization between the atoms and the electronic origin of the site occupancy and instability of the underlying bcc structures. By making calculations for several different configurations of the Nb-Al system we estimated the strengths of the Nb-Nb and Nb-Al bonds. It is shown that the stability of the underlying bcc phases is directly related to Nb-Nb and Nb-Al first-nearest-neighbor interactions. The first-principles calculations were extended to finite temperature by including various contributions to the free energy. In particular, the vibrational free energy was calculated within the quasiharmonic approximation, and it is shown that the contribution of the low energy modes to the lattice entropy helps to stabilize ordered bcc phases against ω-type phase transformations. Semi-quasi-random structures were employed to study the stability of the ordered and disordered bcc phases. Our study showed, in agreement with experiment, that the ω, ordered, and disordered phases can coexist in a nonequilibrium state at finite temperature.

The thermal conductivity kappa(T) of Si nanostructures containing impurities is calculated from first-principles using nonequilibrium molecular dynamics simulations in thermally "prepared" periodic supercells. For a given concentration of impurities, kappa exhibits strongly nonlinear variations with the mass of the impurity. There is a narrow range of conditions for which kappa is substantially reduced relative to that of the pure material. This suggests that the kappa of nanowire could be controlled with impurities and that nanoregions with a desired kappa could be implanted on chips.

We examine by means of first-principles calculations the bcc-like (bcc: body centered cubic) to ω-like phase transformations in Ti-Al alloys with Nb additions at finite temperature. To simulate the alloy we use different discrete atomic configurations in a six atom unit cell of the stoichiometry Ti(3)Al(2)Nb. Calculated ground state energies show an instability in the ternary Ti(3)Al(2)Nb alloy against the ω structure type atomic displacement. To better understand the role of entropy in the stability/instability of these systems, the first-principles calculations are extended to finite temperature by including various contributions to the free energy. In particular, the vibrational free energy is calculated within a quasiharmonic approximation. It is shown that the bcc structure is stabilized by the contribution of the low energy modes to the lattice entropy against ω type atomic displacements. We find that configurational entropy plays a major role in the ω to B8(2) transformation. Calculated lattice parameters and transition temperatures are found to be in excellent agreement with experiment.

The vibrational lifetimes and decay channels of local vibrational modes are calculated from first principles at various temperatures. Our method can be used to predict the temperature dependence of the lifetime of any normal mode in any crystal. We focus here on the stretch modes of H2*, H+(BC), and VH x HV in Si. The frequencies are almost identical, but the lifetimes vary from 4 to 295 ps. The calculations correctly predict the lifetimes for T > 50 K and illustrate the critical importance of pseudolocal modes in the decay processes of high-frequency local vibrational modes.

We explore the detection of paraoxon, a model compound for nonvolatile organophosphate nerve agents such as VX. The detection utilizes europium complexes with 1,10 phenanthroline and thenoyltrifluoroacetone as sensitizing ligands. Both europium luminescence quenching and luminescence enhancement modalities are involved in the detection, which is simple, rapid, and sensitive. It is adaptable as well to the more volatile fluorophosphate nerve agents. It involves nothing more than visual luminescence observation under sample illumination by an ordinary hand-held ultraviolet lamp.

We report a photoluminescence-based field method for detecting traces of explosives. In its standard version, the method utilizes a commercially available color spot test kit for treating explosive traces on filter paper after swabbing. The colored products are fluorescent under illumination with a laser that operates on three C-size flashlight batteries and delivers light at 532 nm. In the fluorescence detection mode, by visual inspection, the typical sensitivity gain is a factor of 100. The method is applicable to a wide variety of explosives. In its time-resolved version, intended for in situ work, explosives are tagged with europium complexes. Instrumentation-wise, the time-resolved detection, again visual, can be accomplished in facile fashion. The europium luminescence excitation utilizes a laser operating at 355 nm. We demonstrate the feasibility of CdSe quantum dot sensitization of europium luminescence for time-resolved purposes. This would allow the use of the above 532 nm laser.

Pseudolocal vibrational modes (pLVMs) are defect-related vibrational modes which are localized despite being below the phonon maximum. Such modes are sometimes seen as phonon replicas in photoluminescence spectra. The pLVMs associated with two copper-related defects are calculated from first-principles density-functional theory in periodic supercells. The localization of the pLVMs is quantified using the magnitude of the eigenvectors of the dynamical matrix.

The concept of utilizing photoluminescent semiconductor nanocrystals for latent fingerprint detection, especially in concert with phase-resolved imaging for background fluorescence suppression, is reduced to practice with CdS nanocrystals that are capped with dioctyl sulfosuccinate. The nanocrystals are dissolved in heptane or hexane and are applied in much the same way as staining with fluorescent dye, on articles that have been pre-fumed with cyanoacrylate ester and also on the sticky side of electrical tape without pre-fuming. Since CdS can form a photoluminescent nanocomposite with dendrimers, a feasibility examination of dendrimer tagging of fingerprints has also been conducted.

A lipid-specific europium-based chemistry for the detection of latent fingerprints is presented. The applicability of the method to both porous and smooth surfaces, its basis of covalent reaction with lipids, the absence of chlorofluorocarbon carrier solvent, cost, and development speed are all factors that imply that the approach will become a major fingerprint detection method. Other potential forensic applications of this type of chemistry include DNA profiling.

The bilayer stability of liposomes containing unsaturated phosphatidylethanolamine (PE) has been investigated by measuring the C = O and CH2 stretching frequencies of the lipids at different lipid compositions and temperatures. Binary mixtures of 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) and dilinoleoyl-PE (DLPE) are known to exhibit lamellar liquid crystalline (L alpha), inverted hexagonal (HII) and metastable intermediate (I) phases. Abrupt increases in the C = O and CH2 stretching frequencies at 65-75 and 90-95% PE, respectively, were found as the PE content of the DLPE/POPC mixtures was increased from 0 to 100%. These transitions were associated with the L alpha -I and I-HII phase transitions of the DLPE/POPC mixtures, accordingly. The effects of three lipid perturbants, butylated hydroxytoluene (BHT), diacylglycerol (DG) and cholesterol (CL), on the above L alpha -I and I-HII transitions were also examined. All perturbants were found to be effective in shifting the L alpha -I transition of the DLPC/POPC mixtures to a lower PE% as detected by the C = O stretching frequency measurements. On the other hand, the perturbants appeared to eliminate the I-HII transition of the DLPE/POPC mixtures as detected by the CH2 stretching frequency measurements. The effectiveness of the perturbants in promoting the L alpha -I phase transition of the DLPE/POPC mixtures followed the order of DG > BHT > CL.(ABSTRACT TRUNCATED AT 250 WORDS)

The heterogeneous proton MR relaxation decay process in human brain has been investigated by performing region-of-interest and pixel-by-pixel calculations on the multiecho MR images with different repetition times (TR) of human brains using a clinical 1.5-T whole-body superconducting MR scanner. Based on the monoexponential, biexponential, and continuous gaussian distribution relaxation models, first-order proton relaxation parameters (proton density, T1 and T2) and higher-order transverse proton relaxation parameters (T2-long, T2-short, T2-long fraction, T2-average, and T2-distribution width) were calculated. On the basis of an F test (p < .01), the statistical significance of the higher-order (biexponential and distribution) fits over the monoexponential fit was evaluated. Here, a significant improvement in the biexponential fit was found for some of the regions containing the ventricular cerebrospinal fluid (CSF) (T2-long = 2780 +/- 570 ms; T2-short = 159 +/- 42 ms; T2-long fraction = 0.51 +/- 0.08 ms) due to the partial volume effect but not for most of the white matter (WM). On the other hand, an improvement of fit to WM was obtained when distribution (T2-average = 80 +/- 8 ms; T2-distribution half-width = 21 +/- 4 ms) as opposed to monoexponential (T2 = 89 +/- 10 ms) fit was used. As internal controls, tubes of CuSO4 solution (T2 = 1293 +/- 128 ms) and agarose gel (T2 = 111 +/- 10 ms) which have similar T2 values as the CSF and WM of the brain, respectively, were attached to the human head and imaged concomitantly. No significance improvements in either the biexponential or distribution fits over the monoexponential fit were found for all the controls. In addition to the first-order and higher-order relaxation parameter maps, the monoexponential chisquares, as well as the chisquares ratio (chisquares of the monoexponential fit divided by that of the higher-order fit), maps were also generated. Unlike the higher-order T2-relaxation parameter maps, the chisquares parameter maps required no selection of any predetermined statistical confidence level. Therefore, these chisquares parameter maps provided a somewhat nonsubjective spatial profile of the heterogeneous transverse relaxation process in the brain. Our results led us to propose that the use of chisquares parameter maps, together with the first-and higher-order relaxation parameter maps, may further improve the in vivo tissue characterization capability of MRI in future clinical diagnosis and staging of intracranial diseases.

The non-Einstein diffusion behavior of water in a model biological tissue system, intact duck embryos, has been investigated by the use of an in vivo proton pulsed-gradient spin-echo (PGSE) MR imaging technique. Multiple-frame MR images of the intact duck embryos and control solution (0.5 mM CuSO4 doped water) were acquired systematically at different diffusion times and strengths of the diffusion-sensitizing magnetic field gradients of the PGSE sequence. These raw images were then used to generate various dynamic (self-diffusion coefficient) and structural (fractal, residual attenuation, and compartment fraction) diffusion parameter maps of water in the imaging objects on the basis of different Einstein and higher order (non-Brownian, Residual, and 2-compartment) diffusion models. The self-diffusion coefficients of the body tissues of the embryos obtained from all diffusion models were significantly lower than those of the surrounding embryonic fluid. The structural diffusion parameter maps obtained from the higher order diffusion models revealed that water molecules exhibited either non-Brownian, restricted, or compartmentalized diffusion behavior in the embryonic tissues, but Einstein or Brownian diffusion behavior in the embryonic fluid and control solution. The diffusion parameter maps, both dynamic and structural, were found to provide much better contrasts than the conventional relaxation time (T1, T2, and biexponential T2) maps in separating the tissues from the surrounding embryonic fluid in the duck embryos. The mathematical models and procedures for generating the dynamic and structural diffusion parameter maps are also presented in this paper.

Fourier transform infrared (FTIR) and time-resolved fluorescence spectroscopy have been employed to examine the structural dynamics of lipid fatty acyl chains and lipid/water interfacial region of a binary lipid mixture containing unsaturated phosphatidylethanolamine (PE) and diacylglycerol (DG). Infrared vibrational frequencies of the CH2 symmetric stretching and the C = O stretching bands of the lipids were measured at different lipid compositions and temperatures. For 0% DG, the lamellar gel to lamellar liquid crystalline (L beta-L alpha) and the L alpha to inverted hexagonal (L alpha-HII) phase transitions were observed at approximately 15 degrees and 55 degrees C, respectively. As the DG content increased gradually from 0% to 15%, the L alpha-HII phase transition temperature decreased drastically while the L beta-L alpha phase transition temperature decreased only slightly. At 10% DG, a merge of these two phase transitions was noticed at approximately 10 degrees C. For the composition study at 23 degrees C, the L alpha-HII transition occurred at approximately 6-10% DG as indicated by abrupt increases in both the CH2 and C = O stretching frequencies at those DG contents. Using time-resolved fluorescence spectroscopy, abrupt decreases in both the normalized long time residual and the initial slope of the anisotropy decay function of lipid probes, 1-palmitoyl-2-[[2-[4-(6-phenyl-trans-1,3,5- hexatrienyl)phenyl]ethyl]carbonyl]-3-sn-phosphatidylcholine, in these PE/DG mixtures were observed at the L alpha-HII phase transition. These changes in the anisotropy decay parameters suggested that the rotational dynamics and orientational packing of the lipids were altered at the composition-induced L alpha-HII transition, and agreed with a previous temperature-induced L alpha-HII transition study on pure unsaturated PE (Cheng (1989) Biophys. J. 55, 1025-1031). The fluorescence lifetime of water soluble probes, 8,1-anilinonapthalenes sulfonate acid, in PE/DG mixtures increased abruptly at the L alpha-HII phase transition, suggesting that the conformation and hydration of the lipid/water interfacial region also undergo significant changes at the L alpha-HII transition.

By the use of frequency domain cross-correlation fluorometry, the fluorescence lifetime of the water soluble probe 8,1-anilinonapthalene sulfonic acid (ANS) in aqueous dispersions of dioleoylphosphatidylethanolamine (DOPE) and phosphatidylethanolamine transphosphatidylated from egg phosphatidylcholine (TPE) was measured. The orientational order parameter and rotational diffusion constant of the lipophilic probe 1-(4-trimethylammoniumphenyl)-6-phenyl-1,3,5-hexatriene (TMA-DPH) were also determined in TPE dispersions. In agreement with a previous study on DOPE (Cheng (1989) Biophys. J. 55, 1025-1031), abrupt changes in both the order packing and rotational diffusion constant were found at the lamellar liquid crystalline (L alpha) to inverted hexagonal (HII) phase transition of TPE. Owing to the subnanosecond resolution capability of this frequency domain fluorometric technique, the heterogeneous fluorescence decay of ANS was resolved into three distinct components with different decay lifetimes (tau's). They were 0 less than tau less than 0.5 ns, 2 less than tau less than 9 ns and tau greater than 15 ns. These lifetime regions were attributed to the partitioning of ANS into the bulk aqueous medium, the lipid/water interface and the lipid hydrocarbon region, respectively. These classifications of lifetime regions were further supported by the sensitivity of those lifetime components with the solvent isotopic shift of D2O. Similar to the changes of orientational order and rotational diffusion of lipophilic probe, the lifetime and intensity fraction of ANS associated with the lipid/water interfacial region declined abruptly at the L alpha-HII transition of both DOPE and TPE. This observation suggested that a dehydration of the lipid headgroup surface occurs at the L alpha-HII transition. This study provided evidence that both the lipid headgroup surface hydration and the lipid dynamics change drastically as a result of the macroscopic rearrangement of lipids at the L alpha-HII transition.

Using purified sarcoplasmic reticulum membranes as model systems, the role of calcium ion in the thermal inactivation of membrane calcium transport was investigated. Hyperthermia induces calcium release from the heavy fraction of sarcoplasmic reticulum. This calcium channel related calcium release was inhibited by the presence of glycerol and enhanced by the presence of ethanol. Calcium was found to protect the thermal-induced calcium transport inactivation of CaATPase in the light fraction of sarcoplasmic reticulum. Both glycerol and cholesterol protect the thermal inactivation of CaATPase. Yet their effects on the calcium-induced protection kinetics were rather different, i.e., the glycerol inserts its protection effect by increasing the degree of cooperativity of calcium binding, while cholesterol increases the calcium-binding affinity. The calcium protection effect was attributed to the ability of calcium to enhance the thermal stability of the protein. This was demonstrated by an upshift (30-39 degrees C) of the transition temperature of the rotational parameter of the native tryptophans of CaATPase in the presence of calcium.

The orientational order and rotational dynamics of 1-palmitoyl-2-[[2-[4-(6-phenyl-trans-1,3,5- hexatrienyl)phenyl]ethyl] carbon yl]-3-sn-phosphatidylcholine (DPH-PC) in dilinoleoylphosphatidylethanolamine (DLPE) and 1-palmitoyl-2-oleoylphosphatidylcholine (POPC) binary lipid mixtures were investigated. A previous study (Biochim. Biophys. Acta 731 (1983) 177) indicated that the empirical phase diagram of POPC/DLPE can roughly be divided into three zones. They are the lamellar (15% PC and higher), intermediate (5-15% PC) and inverted hexagonal (0-5% PC) phases. As the lipids changed from the lamellar to intermediate phase, the order parameter increased at all temperatures (1-50 degrees C). On the contrary, the rotational diffusion decreased at high temperatures (20-50 degrees C) but increased at low temperatures (1-10 degrees C). These results indicate that the intermediate phase is in a stressed state at high temperatures but in a highly mobile amorphous state at low temperatures. As the lipid progressed from the intermediate toward hexagonal phase, the order parameter decreased abruptly at all temperatures. The ratio of order parameter in the intermediate phase to that in the hexagonal phase was calculated. This ratio was found to increase linearly with temperature, indicating that a distinct change in the packing symmetry of lipids occurred as temperature increased. From the intermediate to hexagonal phase, the rotational diffusion increased slightly at high temperatures but declined abruptly at low temperatures. These results further agreed with the stressed and amorphous natures of the intermediate phases as described above.