The Picatinny Arsenal ( or ) is an American military research and manufacturing facility located on 6,400 acres (26 km2) of land in Jefferson and Rockaway Township in Morris County, New Jersey, United States, encompassing Picatinny Lake and Lake Denmark. The Arsenal is the headquarters of the US Army Combat Capabilities Development Command Armaments Center. It is known for developing the ubiquitous Picatinny rail, as well as being the army's center of expertise for small arms cartridge ammunition. The facility was founded in 1880 as the Picatinny Powder Depot. Soon afterward, the navy acquired a portion of the arsenal to establish the Lake Denmark Powder Depot, later known as Lake Denmark Naval Ammunition Depot. It manufactured gunpowder until after World War I, at which time the facility also began producing heavy munitions and grew more involved in research and development activities. During World War II Picatinny was a major large-caliber-round loading plant with 18,000 employees. Today, the facility develops new technologies for the US Armed Forces and builds various munitions, weapons and armor systems. Picatinny Arsenal is also home to the US Army Explosive Ordnance Disposal Technology Directorate. This group is responsible for the creation of tools, equipment, and procedures for US Army EOD personnel. Some of their more recent inventions were the use of weapons on a robot platform and the SWORDS robot. Their building has been recently renamed in honor of one of their deceased soldiers, SFC Scott "Smitty" Smith, who was killed in Iraq in July 2006.
Additively manufactured auxetics (structures exhibiting a negative Poisson's ratio) offer a unique combination of enhanced mechanical strength and energy absorption. These properties can be further improved through strategic material placement and architectural design. This study investigates the feasibility of fabricating bi-material rotating-square auxetic structures composed of flexible and rigid constituents in their squares and hinges. Rotating-square auxetic structures are manufactured via material extrusion using rigid polylactic acid (PLA) and flexible thermoplastic polyurethane (TPU) to explore the effects of material distribution on mechanical performance and failure characteristics at the macro (i.e., component) and meso (i.e., cell) scales. Baseline tests are conducted to quantify single- and bi-material interfacial strength and failure modes under normal, shear, and combined loading conditions. Upon validation of interface integrity, single- and bi-material auxetic structures are fabricated and tested in uniaxial compression. Relative to the TPU single-material structure, the PLA square-TPU hinge structure provides a 33% increase in structural stiffness, increases energy absorption, delays the global densification strain by 10%, yields a structural Poisson's ratio at least 0.3 lower than its single-material counterpart through global axial strains of 20%, and demonstrates partial shape recovery. Multiscale experimental analyses supplemented by a kinematic model reveal the rotation-dependent stiffening mechanisms of these structures, highlighting the benefits of flexible hinge materials. Bi-material structures with flexible hinges are shown to have bilinear trends in structural stiffness and energy absorption, not intrinsic to their single-material counterparts. These findings highlight the potential of bi-material design strategies in advancing the functionality and tunability of auxetic structures for the next generation of mechanical metamaterials.
COVID-19 required educators and students to rapidly move to online learning. Simultaneously, while navigating the pandemic in lockdown, citizens were exposed to the brutal murder of George Floyd. The increased exposure to online activity and discrimination generated a hyperawareness of the potential link between the two. Our interest was to examine that linkage as we considered the prevalence and escalation of online racial discrimination (ORD) as a student phenomenon. Filtering for adolescent and young adult students, this systematic review ultimately employed 21 articles. Our results reflect that ORD as defined, changed over time, as did the ways it manifested. Importantly, the impacts of ORD on student learning and well-being were revealed. This review further indicates that the expansion of online instruction created a complex intersection between online social interactions and academic outcomes ripe for vigilance. Our work adds to the ORD literature while informing future education researchers, educators, and stakeholders of its harmful impacts.
Students rely on information literacy (IL) to effectively assess information. However, we lack understanding about how IL instruction occurs in naturalistic science classrooms. This mixed-methods study provides descriptive accounts of teachers' IL instruction and its responsiveness to students' prior knowledge, using transcripts from 55 lessons with over 2800 minutes of classroom interactions and students' prior IL scores (n = 335). Results suggest that teachers in our sample most often provided instruction on what information is needed and how to use information to fulfill task requirements. While teachers demonstrated overall responsiveness to students' prior knowledge, there was some mismatch among specific IL components.
The failure criterion based on both stress and stress-gradient failure conditions was used to understand and predict the failures of two different scenarios. The first scenario was to understand why a very small hole, compared to the specimen’s dimension, does not affect the failure load even though it still has a high stress concentration at the hole's edge. Both the failure criterion and an experimental study using a high-speed camera consistently showed that failure initiated a small distance away from the hole so that the stress concentration does not affect the failure if the hole is much smaller than the specimen width. The second case of study was perforated specimens loaded by an inserted pin through the holes because the failure characteristics are quite different depending on the loading conditions. Six different types of test specimens were used in the study. The failure stress, failure locations, and initial failure orientations were measured and were also predicted using the failure criterion. Both predicted and measured results agreed well, in general, for all the test specimens even though the failure characteristics of the tested specimens demonstrated pronounced sensitivity to specimen width and hole location.
We developed a low-phase-noise, high-sensitivity linear-frequency-modulated continuous-wave (LFMCW) airborne radar for counter-UAS (unmanned aerial system) applications. It is low in size, weight, power, and cost (SWaP-C) (0.5 kg with batteries, operating for > 4 hours with 2 AA-size batteries) and mountable on a small UAS. It detects small drones in air using patch antennas.
