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Notes: Time-resolved electron diffraction harbors great promise for resolving the fastest chemical processes with atomic level detail. The main obstacles to achieving this real-time view of a chemical reaction are associated with delivering short electron pulses with sufficient electron density to the sample. In this article, the propagation dynamics of femtosecond electron packets in the drift region of a photoelectron gun are investigated with an N-body numerical simulation and mean-field model. It is found that space-charge effects can broaden the electron pulse to many times its original length and generate many eV of kinetic energy bandwidth in only a few nanoseconds. There is excellent agreement between the N-body simulation and the mean-field model for both space-charge induced temporal and kinetic energy distribution broadening. The numerical simulation also shows that the redistribution of electrons inside the packet results in changes to the pulse envelope and the development of a spatially linear axial velocity distribution. These results are important for (or have the potential to impact on) the interpretation of time-resolved electron diffraction experiments and can be used in the design of photoelectron guns and streak tubes with temporal resolution of several hundred femtoseconds. © 2002 American Institute of Physics.

Notes: The refractive index of sapphire at 532 nm has been determined along the Z axis over a range of conditions produced in shock compression and release experiments. In these experiments, a laser interferometer is used to measure particle velocity at an interface with a sapphire window. Values for refractive index are found from velocity corrections that must be made to account for refractive-index changes in the window due to shock wave motion. Early studies found that Z-cut sapphire windows resulted in much larger corrections than other window materials. These studies examined refractive-index changes at a wavelength of 633 nm, corresponding to the helium-neon lasers typically used in interferometers at that time. Because of the high shock impedance of sapphire, its use as an interferometer window since the early studies has been limited. Recent interest in the shock response of high-impedance ceramics, however, has resulted in considerable use of sapphire windows in experiments using laser interferometers operating at a wavelength of 532 nm. The current study is a careful re-examination of the refractive index of Z-cut sapphire under shock compression and release at this wavelength. As in the earlier work, symmetric-impact experiments were conducted on a gas gun facility using sapphire discs cut with their faces normal to the Z axis of the crystal. Laser interferometer measurements were made under known conditions to find the necessary velocity corrections as a function of the shocked state. A method used previously for analyzing refractive-index effects was used to determine refractive index as a function of the shocked state during single-shock motion, then extended to later events involving additional wave motions within the window. The current refractive-index measurements show a simple, linear dependence on density in the shocked state, in contrast to a more complicated dependence found previously. This difference is shown to be a consequence of small changes in the measured velocity corrections. The polarizability behavior is also examined using the present results, indicating a near balance between refractive-index changes due strictly to increasing density and those resulting from polarizability changes in the shocked state. An analysis using available sapphire data on refractive-index changes during hydrostatic compression and isobaric heating indicates that the temperature dependence of the polarizability has a relatively small effect on the changes in refractive index during shock compression. Together with the linear index–density relation, this indicates that a simple velocity correction found for single-shock motion can be accurately applied to arbitrary wave motions within sapphire windows. © 2002 American Institute of Physics.

Notes: External liberalization—the relaxation of restrictions on cross-border trade and inbound direct investment—has played an important role in the programs of economic transition in central Europe. While liberalization is widely heralded, there has been little empirical analysis of the links between liberalization and industry structure. This analysis examines changes in foreign presence following external liberalization in Poland and Hungary. I show that the presence of proprietary and intangible assets explains much of the cross-industry variation in patterns of foreign presence and, for a given level of foreign presence, whether this will occur via trade or inbound direct investment.

Notes: The hypercatabolism after massive pediatric burns has been effectively treated with recombinant human growth hormone, an anabolic agent that stimulates protein synthesis and abrogates growth arrest. While experimental studies have shown increased potential for fibrosis induced by growth hormone therapy, adverse effects on human scars have not been investigated. Our aim was to evaluate hypertrophic scar formation in 62 patients randomized to receive injections of 0.05 mg/kg/day of recombinant human growth hormone or placebo, from discharge until 1 year after burn. Scar scales were used to evaluate scar-severity at discharge, 6, 9, 12, and 18–24 months after burn, by three observers blinded to treatment. Computer-assisted planimetry allowed quantification of percentage of hypertrophic scar formation. Types I and III collagens were localized and quantified in scars and normal skin of patients from both groups, using immunohistochemistry with confocal laser microscopy analysis. Insulin-like growth factor-1 blood levels helped assess compliance. Statistical analysis showed that scar hypertrophy significantly increased from 6 to 12 months after injury in both groups, while decreasing at 18–24 months postburn. Types I and III collagens were statistically increased in the reticular layer of scars from both groups when compared to paired normal skin. Insulin-like growth factor-1 was significantly increased in the recombinant human growth factor-treated group. No differences were seen when recombinant human growth factor and control groups were compared using the scar scales, planimetry, or immunohistochemistry. We concluded that recombinant human growth hormone therapy did not adversely affect scar formation and should not contraindicate the administration of recombinant human growth hormone as a therapeutic approach to severely burned children.

Notes: Severe burns cause not only skin injury but several marked systemic derangements. During wound healing, matrix metalloproteinases (MMPs) and the tissue inhibitors of metalloproteinases play an important role in tissue regeneration and remodeling processes. Therefore, in the present study, we determined the serum levels of MMPs and tissue inhibitor of metalloproteinase-1 in burn patients over time. Serum samples from 12 severely burned children (mean age 7.9 ± 2.5 years) with 〉40% total body surface area burns were obtained within 0.5 hours, 3, 7, and 21 days after injury. Pro-MMP-1, MMP-3, MMP-9, and tissue inhibitor of metalloproteinase-1 serum levels were assayed by enzyme-linked immunoassay and compared to normal healthy volunteers. Two-way analysis of variance and Bonferroni's test were used for statistical analysis. Pro-MMP-1 levels in the serum were significantly elevated by the seventh day after burn. MMP-3 and MMP-9 levels showed significant increases by day 3 and 21 compared to normals, respectively. Tissue inhibitor of metalloproteinase-1 levels did not change with time after burn but were significantly higher by 3 days after burn compared to normal serum. In conclusion, changes in MMPs and tissue inhibitor of metalloproteinase-1 occur in burn patients and those changes may be a mechanism beneficial to wound healing. (WOUND REP REG 2003;11:177–180)

Notes: There is a plethora of new silver containing dressings on the market today. Various manufacturers attempt to show that their dressings are the most efficacious and therefore should be preferentially employed by health care workers based on the results of their in vitro tests. However, there have been no studies to date that clearly identify which in vitro tests are appropriate for comparison purposes. The available literature suggests that there are problems with disc sensitivity assays in terms of assessing the antimicrobial efficacy of silver. Spadaro (1985) has shown that the diameters of zones of inhibition were not proportional to the concentration of anodic silver in complex test media. Further, Richards et al (2001) have shown that zones of inhibition did not appear to correlate to log reduction assay data for silver containing dressings. Other authors favour log reduction or time kill assays as they better compare to clinical data. The purpose of this study was to determine which in vivo test is most appropriate for evaluating the antimicrobial efficacy of silver-containing dressings. This was done by testing 8 different silver containing dressings and 2 non-silver (mafenide acetate or hexamethylene biguanide) containing topical agents against 17 clinically relevant microorganisms using both zone of inhibition assays and time-kill kinetic assays in complex media. The results for the two assays were then correlated to determine if the methods generated similar results. It was determined that the two methods do not correlate at all. This is most likely a result of the silver interacting with the media in the zone of inhibition test, thus invalidating the results of this test. We therefore conclude that zone of inhibition data generated for silver-containing dressings is of little value when assessing antimicrobial efficacy, and that time-kill assays are of greater use.

Notes: A porcine model of wound healing was employed to examine the impact of nanocrystalline silver–coated dressings on specific wound healing events. Full-thickness wounds were created on the backs of pigs, contaminated with an experimental inoculum containing Pseudomonas aeruginosa, Fusobacterium sp., and coagulase-negative staphylococci, and covered with dressing products either containing silver or not. Nanocrystalline silver-coated dressings promoted rapid wound healing, particularly during the first several days post-injury. Healing was characterized by rapid development of well vascularized granulation tissue that supported tissue grafting 4 days post-injury, unlike control dressed wounds. The proteolytic environment of wounds treated with nanocrystalline silver was characterized by reduced levels of matrix metalloproteinases. Matrix metalloproteinases have been shown to be present in chronic ulcers at abnormally high levels, as compared with acute wounds, and may contribute to the nonhealing nature of these wounds. Cellular apoptosis occurred at a higher frequency in the nanocrystalline silver–treated wounds than in wounds dressed with other products. The results suggest that nanocrystalline silver may play a role in altering or compressing the inflammatory events in wounds and facilitating the early phases of wound healing. These benefits are associated with reduced local matrix metalloproteinase levels and enhanced cellular apoptosis. (WOUND REP REG 2002;10:)

Notes: External liberalization—the relaxation of restrictions on cross-border trade and inbound direct investment—has played an important role in the programs of economic transition in central Europe. While liberalization is widely heralded, there has been little empirical analysis of the links between liberalization and industry structure. This analysis examines changes in foreign presence following external liberalization in Poland and Hungary. I show that the presence of proprietary and intangible assets explains much of the cross-industry variation in patterns of foreign presence and, for a given level of foreign presence, whether this will occur via trade or inbound direct investment.

Notes: Purpose: The purpose of this investigation was to evaluate and compare the mechanical and thermal properties of 6 commonly used polymethyl methacrylate denture base resins. Materials and Methods: Sorption, solubility, color stability, adaptation, flexural stiffness, and hardness were assessed to determine compliance with ADA Specification No. 12. Thermal assessments were performed using differential scanning calorimetry and dynamic mechanical analysis. Results were assessed using statistical and observational analyses. Results: All materials satisfied ADA requirements for sorption, solubility, and color stability. Adaptation testing indicated that microwave-activated systems provided better adaptation to associated casts than conventional heat-activated resins. According to flexural testing results, microwaveable resins were relatively stiff, while rubber-modified resins were more flexible. Differential scanning calorimetry indicated that microwave-activated systems were more completely polymerized than conventional heat-activated materials. Conclusion: The microwaveable resins displayed better adaptation, greater stiffness, and greater surface hardness than other denture base resins included in this investigation. Elastomeric toughening agents yielded decreased stiffness, decreased surface hardness, and decreased glass transition temperatures.

Notes: Intracellular calcium is increased in vulnerable spinal motoneurons in immune-mediated as well as transgenic models of amyotrophic lateral sclerosis (ALS). To determine whether intracellular calcium levels are influenced by the calcium-binding protein parvalbumin, we developed transgenic mice overexpressing parvalbumin in spinal motoneurons. ALS immunoglobulins increased intracellular calcium and spontaneous transmitter release at motoneuron terminals in control animals, but not in parvalbumin overexpressing transgenic mice. Parvalbumin transgenic mice interbred with mutant SOD1 (mSOD1) transgenic mice, an animal model of familial ALS, had significantly reduced motoneuron loss, and had delayed disease onset (17%) and prolonged survival (11%) when compared with mice with only the mSOD1 transgene. These results affirm the importance of the calcium binding protein parvalbumin in altering calcium homeostasis in motoneurons. The increased motoneuron parvalbumin can significantly attenuate the immune-mediated increases in calcium and to a lesser extent compensate for the mSOD1-mediated ‘toxic-gain-of-function’ in transgenic mice.