Fighting Back: Crime, Self-Defense, and the Right to Carry a Handgun

Ten years ago this month, a controversial "concealed- carry" law went into effect in the state of Florida. In a sharp break from the conventional wisdom of the time, that law allowed adult citizens to carry concealed firearms in public. Many people feared the law would quickly lead to disaster: blood would literally be running in the streets. Now, 10 years later, it is safe to say that those dire predictions were completely unfounded. Indeed, the debate today over concealed-carry laws centers on the extent to which such laws can actually reduce the crime rate.To the shock and dismay of gun control proponents, concealed-carry reform has proven to be wildly popular among state lawmakers. Since Florida launched its experiment with concealed-carry in October 1987, 23 states have enacted similar laws, with positive results.Prior to 1987, almost every state in America either prohibited the carrying of concealed handguns or permitted concealed-carry under a licensing system that granted government officials broad discretionary power over the decision to grant a permit. The key feature of the new concealed-carry laws is that the government must grant the permit as soon as any citizen can satisfy objective licensing criteria.Concealed-carry reform reaffirms the basic idea that citizens have the right to defend themselves against criminal attack. And since criminals can strike almost anywhere at any time, the last thing government ought to be doing is stripping citizens of the most effective means of defending themselves. Carrying a handgun in public may not be for everyone, but it is a right that government ought to respect

Transport property analysis method for thermoelectric materials: material quality factor and the effective mass model

Thermoelectric semiconducting materials are often evaluated by their figure-of-merit, zT. However, by using zT as the metric for showing improvements, it is not immediately clear whether the improvement is from an enhancement of the inherent material property or from optimization of the carrier concentration. Here, we review the quality factor approach which allows one to separate these two contributions even without Hall measurements. We introduce practical methods that can be used without numerical integration. We discuss the underlying effective mass model behind this method and show how it can be further advanced to study complex band structures using the Seebeck effective mass. We thereby dispel the common misconception that the usefulness of effective band models is limited to single parabolic band materials.Comment: 5 pages, 3 figure

Arresting Children: Examining Recent Trends in Preteen Crime

Are juvenile offenders getting younger? The American public often hears policymakers and justice practitioners assert that young people are committing crimes at younger and younger ages. Is this true? This analysis explores this question by examining data collected by law enforcement agencies across the country. It tracks juvenile crime patterns from 1980 through 2006 and finds that the age profile of juvenile offenders has not changed substantially in 25 years. Crime rates among children under age 13 have generally followed the same crime patterns exhibited among older youth. In a few offense categories, however, increases in preteen crime have outpaced increases among older juveniles, particularly sexual offenses, assaults, and weapons possession (not necessarily firearms). The fact that school authorities and family members often report these offenses suggests a possible hypothesis to explain increases in some preteen crimes: The juvenile justice system today may be dealing with child behavior problems that were once the responsibility of social welfare agencies, schools, and families

Evaluation of true interlamellar spacing from microstructural observations

A method for evaluating true interlamellar spacing from micrographs is proposed for a multidomained lamellar structure. The microstructure of these materials is assumed to be composed of many domains with the lamellae aligned roughly parallel to each other within each domain and with the domains themselves randomly oriented relative to one another. An explicit expression for the distribution of apparent interlamellar spacing is derived assuming that the distribution of the true interlamellar spacing is Gaussian. The average interlamellar spacing is close to the peak interlamellar spacing observed in the distribution. The theoretical distributions are compared with experimental ones obtained by analyzing micrographs of PbTe–Sb2Te3 lamellar composites

Zone Leveling Crystal Growth of Thermoelectric PbTe Alloys with Sb_(2)Te_3 Widmanstätten Precipitates

Unidirectional solidification of PbTe-rich alloys in the pseudobinary PbTe-Sb_(2)Te_3 system using the zone leveling technique enables the production of large regions of homogeneous solid solutions for the formation of precipitate nanocomposites as compared with Bridgman solidification. (PbTe)_(0.940)(Sb_(2)Te_3)_(0.060) and (PbTe)_(0.952)(Sb_(2)Te_3)_(0.048) alloys were successfully grown using (PbTe)_(0.4)(Sb_(2)Te_3)_(0.6) and (PbTe)_(0.461)(Sb_(2)Te_3)_(0.539) as seed alloys, respectively, with 1 mm h^(–1) withdrawal velocity. In the unidirectionally solidified regions of both alloys, Widmanstatten precipitates are formed due to the decrease in solubility of Sb_(2)Te_3 in PbTe. To determine the compositions of the seed alloys for the zone leveling experiments, the solute distribution in solidification in the PbTe-richer part of the pseudobinary PbTe-Sb_(2)Te_3 system has been examined from the concentration profiles in the samples unidirectionally solidified by the Bridgman method

Phonon engineering through crystal chemistry

Mitigation of the global energy crisis requires tailoring the thermal conductivity of materials. Low thermal conductivity is critical in a broad range of energy conversion technologies, including thermoelectrics and thermal barrier coatings. Here, we review the chemical trends and explore the origins of low thermal conductivity in crystalline materials. A unifying feature in the latest materials is the incorporation of structural complexity to decrease the phonon velocity and increase scattering. With this understanding, strategies for combining these mechanisms can be formulated for designing new materials with exceptionally low thermal conductivity

Rapid consolidation of powdered materials by induction hot pressing

A rapid hot press system in which the heat is supplied by RF induction to rapidly consolidate thermoelectric materials is described. Use of RF induction heating enables rapid heating and consolidation of powdered materials over a wide temperature range. Such rapid consolidation in nanomaterials is typically performed by spark plasma sintering (SPS) which can be much more expensive. Details of the system design, instrumentation, and performance using a thermoelectric material as an example are reported. The Seebeck coefficient, electrical resistivity, and thermal diffusivity of thermoelectric PbTe material pressed at an optimized temperature and time in this system are shown to agree with material consolidated under typical consolidation parameters

Zintl Chemistry for Designing High Efficiency Thermoelectric Materials

Zintl phases and related compounds are promising thermoelectric materials; for instance, high zT has been found in Yb_(14)MnSb_(11), clathrates, and the filled skutterudites. The rich solid-state chemistry of Zintl phases enables numerous possibilities for chemical substitutions and structural modifications that allow the fundamental transport parameters (carrier concentration, mobility, effective mass, and lattice thermal conductivity) to be modified for improved thermoelectric performance. For example, free carrier concentration is determined by the valence imbalance using Zintl chemistry, thereby enabling the rational optimization of zT. The low thermal conductivity values obtained in Zintl thermoelectrics arise from a diverse range of sources, including point defect scattering and the low velocity of optical phonon modes. Despite their complex structures and chemistry, the transport properties of many modern thermoelectrics can be understood using traditional models for heavily doped semiconductors

Effective thermal conductivity of polycrystalline materials with randomly oriented superlattice grains

A model has been established for the effective thermal conductivity of a bulk polycrystal made of randomly oriented superlattice grains with anisotropic thermal conductivity. The in-plane and cross-plane thermal conductivities of each superlattice grain are combined using an analytical averaging rule that is verified using finite element methods. The superlattice conductivities are calculated using frequency dependent solutions of the Boltzmann transport equation, which capture greater thermal conductivity reductions as compared to the simpler gray medium approximation. The model is applied to a PbTe/Sb_2Te_3 nanobulk material to investigate the effects of period, specularity, and temperature. The calculations show that the effective thermal conductivity of the polycrystal is most sensitive to the in-plane conductivity of each superlattice grain, which is generally four to five times larger than the cross-plane conductivity of a grain. The model is compared to experimental measurements of the same system for periods ranging from 287 to 1590 nm and temperatures from 300 to 500 K. The comparison suggests that the effective specularity increases with increasing annealing temperature and shows that these samples are in a mixed regime where both Umklapp and boundary scattering are important