458 research outputs found
Standard and derived Planck quantities: selected analysis and derivations
We provide an overview of the fundamental units of physical quantities
determined naturally by the values of fundamental constants of nature. We
discuss a comparison between the 'Planck units', now widely used in theoretical
physics and the pre-quantum 'Stoney units' in which, instead of the Planck
constant, the charge of the electron is used with very similar quantitative
results. We discuss some of the physical motivation for these special units,
attributed much after they were introduced, and also put forth a summary of the
arguments supporting various cases for making specific physical interpretations
of the meanings of some of these units. The new aspects we discuss are a
possible physical basis for the Stoney units, their link to the Planck units,
and also the importance of Planck units for thermodynamical quantities in the
context of quantum gravity.Comment: 22 pages, 1 tabl
Recommended from our members
Pre-Travel Preparation of US Travelers Going Abroad to Provide Humanitarian Service, Global TravEpiNet 2009–2011
We analyzed characteristics of humanitarian service workers (HSWs) seen pre-travel at Global TravEpiNet (GTEN) practices during 2009–2011. Of 23,264 travelers, 3,663 (16%) travelers were classified as HSWs. Among HSWs, 1,269 (35%) travelers were medical workers, 1,298 (35%) travelers were non-medical service workers, and 990 (27%) travelers were missionaries. Median age was 29 years, and 63% of travelers were female. Almost one-half (49%) traveled to 1 of 10 countries; the most frequent destinations were Haiti (14%), Honduras (8%), and Kenya (6%). Over 90% of travelers were vaccinated for or considered immune to hepatitis A, typhoid, and yellow fever. However, for hepatitis B, 292 (29%) of 990 missionaries, 228 (18%) of 1,298 non-medical service workers, and 76 (6%) of 1,269 medical workers were not vaccinated or considered immune. Of HSWs traveling to Haiti during 2010, 5% of travelers did not receive malaria chemoprophylaxis. Coordinated efforts from HSWs, HSW agencies, and clinicians could reduce vaccine coverage gaps and improve use of malaria chemoprophylaxis
Aircraft design at the Naval Postgraduate School - Tactical waverider/long-range cargo aircraft
Aircraft Design, Systems, and Operations Meeting, 09 August 1993 - 11 August 1993The article of record as published may be located at https://doi.org/10.2514/6.1993-4007The graduate program of the Department of Aeronautics and Astronautics at the Naval Postgraduate School uniquely supports a comprehensive design program in aircraft, spacecraft, missile, helicopter, and engine design. This paper is focused on four aircraft configuration designs proposed by AA 4273 Military Aircraft Design course team members. The AA 4273 course is, in turn, supported by a growing research program to enhance and further develop the methodology of aircraft design. This design effort has received considerable support from the NASA/USRA Advanced Design Program in Aeronautics. Specifically, two design solutions for a long-range,carrier based, tactical, wave-rider configured fighter/interceptor aircraft are reviewed herein, as are two solutions for a global range military transport. Both types of aircraft were developed as a graduate student team response to specific design RFPs
Cosmological Analogues of the Bartnik--McKinnon Solutions
We present a numerical classification of the spherically symmetric, static
solutions to the Einstein--Yang--Mills equations with cosmological constant
. We find three qualitatively different classes of configurations,
where the solutions in each class are characterized by the value of
and the number of nodes, , of the Yang--Mills amplitude. For sufficiently
small, positive values of the cosmological constant, \Lambda < \Llow(n), the
solutions generalize the Bartnik--McKinnon solitons, which are now surrounded
by a cosmological horizon and approach the deSitter geometry in the asymptotic
region. For a discrete set of values , the solutions are topologically --spheres, the ground state
being the Einstein Universe. In the intermediate region, that is for
\Llow(n) < \Lambda < \Lhig(n), there exists a discrete family of global
solutions with horizon and ``finite size''.Comment: 16 pages, LaTeX, 9 Postscript figures, uses epsf.st
Inhalation developmental toxicology studies: Teratology study of acetone in mice and rats: Final report
Acetone, an aliphatic ketone, is a ubiquitous industrial solvent and chemical intermediate; consequently, the opportunity for human exposure is high. The potential for acetone to cause developmental toxicity was assessed in Sprague-Dawley rats exposed to 0, 440, 2200, or 11000 ppm, and in Swiss (CD-1) mice exposed to 0, 440, 2200, and 6600 ppm acetone vapors, 6 h/day, 7 days/week. Each of the four treatment groups consisted of 10 virgin females (for comparison), and approx.32 positively mated rats or mice. Positively mated mice were exposed on days 6-17 of gestation (dg), and rats on 6-19 dg. The day of plug or sperm detection was designated as 0 dg. Body weights were obtained throughout the study period, and uterine and fetal body weights were obtained at sacrifice (rats, 20 dg; mice, 18 dg). Implants were enumerated and their status recorded. Live fetuses were sexed and examined for gross, visceral, skeletal, and soft-tissue craniofacial defects. 46 refs., 6 figs., 27 tabs
Variable Curvature Slab Molecular Dynamics as a Method to Determine Surface Stress
A thin plate or slab, prepared so that opposite faces have different surface
stresses, will bend as a result of the stress difference. We have developed a
classical molecular dynamics (MD) formulation where (similar in spirit to
constant-pressure MD) the curvature of the slab enters as an additional
dynamical degree of freedom. The equations of motion of the atoms have been
modified according to a variable metric, and an additional equation of motion
for the curvature is introduced. We demonstrate the method to Au surfaces, both
clean and covered with Pb adsorbates, using many-body glue potentials.
Applications to stepped surfaces, deconstruction and other surface phenomena
are under study.Comment: 16 pages, 8 figures, REVTeX, submitted to Physical Review
In Situ Measurements of Stress Evolution in Silicon Thin Films During Electrochemical Lithiation and Delithiation
We report in situ measurements of stress evolution in a silicon thin-film
electrode during electrochemical lithiation and delithiation by using the
Multi-beam Optical Sensor (MOS) technique. Upon lithiation, due to substrate
constraint, the silicon electrode initially undergoes elastic deformation,
resulting in rapid rise of compressive stress. The electrode begins to deform
plastically at a compressive stress of ca. -1.75 GPa; subsequent lithiation
results in continued plastic strain, dissipating mechanical energy. Upon
delithiation, the electrode first undergoes elastic straining in the opposite
direction, leading to a tensile stress of ca. 1 GPa; subsequently, it deforms
plastically during the rest of delithiation. The plastic flow stress evolves
continuously with lithium concentration. Thus, mechanical energy is dissipated
in plastic deformation during both lithiation and delithiation, and it can be
calculated from the stress measurements; we show that it is comparable to the
polarization loss. Upon current interrupt, both the film stress and the
electrode potential relax with similar time-constants, suggesting that stress
contributes significantly to the chemical potential of lithiated-silicon.Comment: 12 pages, 3 figure
Fatigue testing of three peristernal median sternotomy closure techniques
Failure of a sternotomy closure because of closure system fatigue is a complication that may result in dehiscence and put the individual at risk for serious complications. The purpose of this study was to assess the fatigue performance of three peristernal median sternotomy closure techniques (figure-of-eight stainless-steel wires, figure-of-eight stainless-steel cables, or Pectofix Dynamic Sternal Fixation [DSF] stainless-steel plates) in order to quantify the potential risk of fatigue failure of these devices when subject to cyclic loads in physiologically relevant loading directions
Measurement of Contractile Stress Generated by Cultured Rat Muscle on Silicon Cantilevers for Toxin Detection and Muscle Performance Enhancement
Background: To date, biological components have been incorporated into MEMS devices to create cell-based sensors and assays, motors and actuators, and pumps. Bio-MEMS technologies present a unique opportunity to study fundamental biological processes at a level unrealized with previous methods. The capability to miniaturize analytical systems enables researchers to perform multiple experiments in parallel and with a high degree of control over experimental variables for high-content screening applications.Methodology/Principal Findings: We have demonstrated a biological microelectromechanical system (BioMEMS) based on silicon cantilevers and an AFM detection system for studying the physiology and kinetics of myotubes derived from embryonic rat skeletal muscle. It was shown that it is possible to interrogate and observe muscle behavior in real time, as well as selectively stimulate the contraction of myotubes with the device. Stress generation of the tissue was estimated using a modification of Stoney's equation. Calculated stress values were in excellent agreement with previously published results for cultured myotubes, but not adult skeletal muscle. Other parameters such as time to peak tension (TPT), the time to half relaxation (KRT) were compared to the literature. It was observed that the myotubes grown on the BioMEMS device, while generating stress magnitudes comparable to those previously published, exhibited slower TPT and KRT values. However, growth in an enhanced media increased these values. From these data it was concluded that the myotubes cultured on the cantilevers were of an embryonic phenotype. The system was also shown to be responsive to the application of a toxin, veratridine.Conclusions/Significance: The device demonstrated here will provide a useful foundation for studying various aspects of muscle physiology and behavior in a controlled high-throughput manner as well as be useful for biosensor and drug discovery applications
Modified cantilever arrays improve sensitivity and reproducibility of nanomechanical sensing in living cells
Mechanical signaling involved in molecular interactions lies at the heart of materials science and biological systems, but the mechanisms involved are poorly understood. Here we use nanomechanical sensors and intact human cells to provide unique insights into the signaling pathways of connectivity networks, which deliver the ability to probe cells to produce biologically relevant, quantifiable and reproducible signals. We quantify the mechanical signals from malignant cancer cells, with 10 cells per ml in 1000-fold excess of non-neoplastic human epithelial cells. Moreover, we demonstrate that a direct link between cells and molecules creates a continuous connectivity which acts like a percolating network to propagate mechanical forces over both short and long length-scales. The findings provide mechanistic insights into how cancer cells interact with one another and with their microenvironments, enabling them to invade the surrounding tissues. Further, with this system it is possible to understand how cancer clusters are able to co-ordinate their migration through narrow blood capillaries
- …