Rapid reversion from monomer to dimer regenerates the ultraviolet-B photoreceptor UV RESISTANCE LOCUS8 in intact arabidopsis plants

Arabidopsis (Arabidopsis thaliana) UV RESISTANCE LOCUS8 (UVR8) is a photoreceptor that specifically mediates photomorphogenic responses to ultraviolet (UV)-B in plants. UV-B photoreception induces the conversion of the UVR8 dimer into a monomer that interacts with the CONSTITUTIVELY PHOTOMORPHOGENIC1 (COP1) protein to regulate gene expression. However, it is not known how the dimeric photoreceptor is regenerated in plants. Here, we show, by using inhibitors of protein synthesis and degradation via the proteasome, that the UVR8 dimer is not regenerated by rapid de novo synthesis following destruction of the monomer. Rather, regeneration occurs by reversion from the monomer to the dimer. However, regeneration of dimeric UVR8 in darkness following UV-B exposure occurs much more rapidly in vivo than in vitro with illuminated plant extracts or purified UVR8, indicating that rapid regeneration requires intact cells. Rapid dimer regeneration in vivo requires protein synthesis, the presence of a carboxyl-terminal 27-amino acid region of UVR8, and the presence of COP1, which is known to interact with the carboxyl-terminal region. However, none of these factors can account fully for the difference in regeneration kinetics in vivo and in vitro, indicating that additional proteins or processes are involved in UVR8 dimer regeneration in vivo

Comparison of measured temperatures, thermal stresses and creep residues with predictions on a built-up titanium structure

Temperature, thermal stresses, and residual creep stresses were studied by comparing laboratory values measured on a built-up titanium structure with values calculated from finite-element models. Several such models were used to examine the relationship between computational thermal stresses and thermal stresses measured on a built-up structure. Element suitability, element density, and computational temperature discrepancies were studied to determine their impact on measured and calculated thermal stress. The optimum number of elements is established from a balance between element density and suitable safety margins, such that the answer is acceptably safe yet is economical from a computational viewpoint. It is noted that situations exist where relatively small excursions of calculated temperatures from measured values result in far more than proportional increases in thermal stress values. Measured residual stresses due to creep significantly exceeded the values computed by the piecewise linear elastic strain analogy approach. The most important element in the computation is the correct definition of the creep law. Computational methodology advances in predicting residual stresses due to creep require significantly more viscoelastic material characterization

An Elementary Treatment of the Reverse Sprinkler

We discuss the reverse sprinkler problem: How does a sprinkler turn when submerged and made to suck in water? We propose a solution that requires only a knowledge of mechanics and fluid dynamics at the introductory university level. We argue that as the flow of water starts, the sprinkler briefly experiences a torque that would make it turn toward the incoming water, while as the flow of water ceases it briefly experiences a torque in the opposite direction. No torque is expected when water is flowing steadily into it unless dissipative effects, such as viscosity, are considered. Dissipative effects result in a small torque that would cause the sprinkler arm to accelerate toward the steadily incoming water. Our conclusions are discussed in light of an analysis of forces, conservation of angular momentum, and the experimental results reported by others. We review the conflicting published treatments of this problem, some of which have been incorrect and many of which have introduced complications that obscure the basic physics involved.Comment: 16 pages, 8 figures. The subject of this paper is often referred to in the literature as the "Feynman sprinkler" or the "Feynman inverse sprinkler." v2:references added, discussion of angular momentum conservation clarified, section III expanded to include consideration of dissipative phenomena such as viscosity. v3:minor corrections of style. To appear in the American Journal of Physic

Effect of creep in titanium alloy Ti-6Al-4V at elevated temperature on aircraft design and flight test

Short-term compressive creep tests were conducted on three titanium alloy Ti-6Al-4V coupons at three different stress levels at a temperature of 714 K (825 F). The test data were compared to several creep laws developed from tensile creep tests of available literature. The short-term creep test data did not correlate well with any of the creep laws obtained from available literature. The creep laws themselves did not correlate well with each other. Short-term creep does not appear to be very predictable for titanium alloy Ti-6Al-4V. Aircraft events that result in extreme, but short-term temperature and stress excursions for this alloy should be approached cautiously. Extrapolations of test data and creep laws suggest a convergence toward predictability in the longer-term situation

A comparison of experimental and calculated thin-shell leading-edge buckling due to thermal stresses

High-temperature thin-shell leading-edge buckling test data are analyzed using NASA structural analysis (NASTRAN) as a finite element tool for predicting thermal buckling characteristics. Buckling points are predicted for several combinations of edge boundary conditions. The problem of relating the appropriate plate area to the edge stress distribution and the stress gradient is addressed in terms of analysis assumptions. Local plasticity was found to occur on the specimen analyzed, and this tended to simplify the basic problem since it effectively equalized the stress gradient from loaded edge to loaded edge. The initial loading was found to be difficult to select for the buckling analysis because of the transient nature of thermal stress. Multiple initial model loadings are likely required for complicated thermal stress time histories before a pertinent finite element buckling analysis can be achieved. The basic mode shapes determined from experimentation were correctly identified from computation

Carnage Interrupted: An Analysis of Fifteen Terrorist Plots against Public Surface Transportation, Research Report 11-20

This report examines 13 terrorist plots against public surface transportation that were uncovered and foiled by authorities between 1997 and 2010 and two failed attempts to carry out attacks. Certainly, this is not the total universe of foiled or failed terrorist plots in these years, but they were selected on the basis of what is known about them and the accessibility of information. The report focuses on terrorist plots in the West. Seven of the 15 plots took place in the United States, and four occurred in the United Kingdom. These two countries figure prominently as targets of terrorism, and in addition, American and British officials have dealt with terrorist plots through publicized arrests and trials, which provide additional information. Although motive was not a criterion in the selection of the plots, all but one involve individuals or groups inspired by al Qaeda’s ideology of violent global jihad against the West. The exception is the 1997 Flatbush plot, in which two terrorists, both of whom had connections with Hamas, angered by events in Palestine, simply wanted to kill as many Jews as possible to express their opposition to U.S. support for Israel. Other sources suggest that the Flatbush plotters wanted to force the release of jailed Islamist terrorists in the United States, including Ramzi Yousef, who participated in the 1993 World Trade Center bombing, and Sheik Omar Abdul-Rahman, who was convicted for his involvement in a plot to carry out additional bombings in New York

Selective Screening of Rail Passengers, MTI 06-07

The threat of another major terrorist attack in the United States remains high, with the greatest danger coming from local extremists inspired by events in the Middle East. Although the United States removed the Taliban government and destroyed al Qaeda’s training camps in Afghanistan, events in Europe and elsewhere have shown that the terrorist network leadership remains determined to carry out further attacks and is capable of doing so. Therefore, the United States must systematically conduct research on terrorist strikes against transportation targets to distill lessons learned and determine the best practices for deterrence, response, and recovery. Those best practices must be taught to transportation and security professionals to provide secure surface transportation for the nation. Studying recent incidents in Europe and Asia, along with other research, will help leaders in the United States learn valuable lessons—from preventing attacks, to response and recovery, to addressing the psychological impacts of attacks to business continuity. Timely distillations of the lessons learned and best practices developed in other countries, once distributed to law enforcement, first responders, and rail- and subway-operating transit agencies, could result in the saving of American lives. This monograph focuses on the terrorist risks confronting public transportation in the United States—especially urban mass transit—and explores how different forms of passenger screening, and in particular, selective screening, can best be implemented to reduce those risks