Browsing by Subject "physics, condensed matter"

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Coherent States In Double Quantum Well Systems
(2011-09) Joglekar, Y.; Kellogg, M.; Milovanovic, M.; Tutuc, E.; Tutuc, Emanuel
Copyright (C) 2011 Yogesh Joglekar et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.
Comparison Of Theory And Measurements Of A Two-Stage Light-Gas Gun
(2009-12) Levinson, S.; Berry, D.; Pedersen, B.; Bless, S.; Levinson, S.; Berry, D.; Pedersen, B.; Bless, S.
A comparison of techniques for obtaining projectile velocity history on a two-stage launcher and discuss gun code accuracy vis-a-vis pressure gauges and the new photonic Doppler velocimetry (PDV) technique is presented. The PDV technique itself is described in a companion paper. The PDV records were differentiated to compute acceleration and, hence, base pressure. Two acceleration episodes are revealed in the data. Base pressure values were compared with measurements from stationary pressure gauges and with predictions of a standard two-stage gun code. The agreement with the pressure gages was satisfactory. Code predictions did not account for the two acceleration stages. However, for the main acceleration episode, the predicted base pressure is in good agreement with the smoothed pressure computed from the PDV record. Both the gauge records and PDV contain short-time pressure spikes which are apparently real. Therefore, use of computed base pressure for projectile design may lead to failures if the projectile is vulnerable to pressure spikes.
Damage Evolution In Ballistic Impact Of Glass Plates
(2009-12) Bless, S. J.; Russell, R.; Berry, D. T.; Levinson, S.; Bless, S. J.; Russell, R.; Berry, D. T.; Levinson, S.
High-velocity impact onto a layered glass target produces a very extensive damage pattern exhibiting many distinct morphologies. High-speed photography reveals failure waves and cracks that move at acoustic velocities. These prompt features evolve into a complex final damage pattern that includes needle fragments around the penetration cavity, radial cracks at mid distance, and dicing cracks near the edges.
Deceleration Of Projectiles In Sand
(2012-03) Bless, S.; Cooper, W.; Watanabe, K.; Peden, R.; Bless, S
Penetration of projectiles was measured for hemispherical and conical nose shapes penetrating granular media. Targets were beds of Ottawa sand and Eglin sand. Projectiles were rigid metals. Experimental parameters that were varied included velocity (from 300 to 600 m/s), nose shape, sand density, and scale (from 5 mm to 20 mm). Strong evidence for scale effects is found: 5 mm diameter projectiles are less effective penetrators than 12.5, 15, or 20 mm diameter penetrators.
Development Of Third Harmonic Generation As A Short Pulse Probe Of Shock Heated Material
(2007-12) Grigsby, W.; Cho, B. I.; Bernstein, A. C.; Quevedo, H. J.; Colvin, J.; Downer, M. C.; Ditmire, T.; Grigsby, W.; Cho, B. I.; Bernstein, A. C.; Quevedo, H. J.; Downer, M. C.; Ditmire, T.
We are studying high-pressure laser produced shock waves in silicon (100). To examine the material dynamics, we are performing pump-probe style experiments utilizing 600 ps and 40 fs laser pulses from a Ti:sapphire laser. Two-dimensional interferometry reveals information about the shock breakout, while third harmonic light generated at the rear surface is used to infer the crystalline state of the material as a function of time. Sustained third harmonic generation (THG) during a similar to 100 kbar shock breakout indicate that the rear surface remains crystalline for at least 3 ns. However, a decrease in THG during a similar to 300 kbar shock breakout suggests a different behavior, which could include a change in crystalline structure.
From Coherent States In Adjacent Graphene Layers Toward Low-Power Logic Circuits
(2011-08) Register, L. F.; Basu, D.; Reddy, D.; Register, Leonard F.; Basu, Dipanjan; Reddy, Dharmendar
Colleagues and we recently proposed a new type of transistor, a Bilayer PseudoSpin Field Effect Transistor (BiSFET), based on many-body coherent states in coupled electron and hole layers in graphene. Here we review the basic BiSFET device concept and ongoing efforts to determine how such a device, which would be far from a drop-in replacement for MOSFETs in CMOS logic, could be used for low-power logic operation, and to model the effects of engineerable device parameters on the formation and gating of interlayer coherent state.
Heterostructures For Realizing Magnon-Induced Spin Transfer Torque
(2012-04) Jayathilaka, P. B.; Monti, M. C.; Markert, J. T.; Miller, C. W.; Monti, M. C.; Markert, J. T.
This work reports efforts fabricating heterostructures of different materials relevant for the realization of magnon-induced spin transfer torques. We find the growth of high-quality magnetite on MgO substrates to be straightforward, while using transition metal buffer layers of Fe, Cr, Mo, and Nb can alter the structural and magnetic properties of the magnetite. Additionally, we successfully fabricated and characterized Py/Cr/Fe3O4 and Fe3O4/Cr/Fe3O4 spin valve structures. For both, we observe a relatively small giant magnetoresistance and confirman inverse dependence on spacer layer thickness. Thus, we have shown certainmaterials combinations that may form the heterostructures that are the building blocks necessary to achieve magnon-induced spin transfer torque devices.
High-Resolution Projectile Velocity And Acceleration Measurement Using Photonic Doppler Velocimetry
(2009-12) Levinson, S.; Satapathy, S.; Levinson, S.; Satapathy, S.
This paper describes the new photonic Doppler velocimetry (PDV) technique for measuring time-resolved projectile velocity and acceleration profiles for full flight of the launch package in a two-stage light-gas gun (LGG). This technique is shown to provide excellent temporal and spatial resolution in measurement. Two non-linear acceleration stages were observed for the first time on the LGG. When the gun bore was at atmospheric pressure, a strong opacity was observed during hypervelocity projectile motion >2200 km/s.
Impact Strength Of Glass And Glass Ceramic
(2009-12) Bless, S.; Tolman, J.; Bless, S.; Tolman, J.
Strength of glass and glass ceramic was measured with a bar impact technique. High-speed movies show regions of tensile and compressive failure. The borosilicatc glass had a compressive strength of at least 2.2 GPa, and the glass ceramic at least 4 GPa. However, the BSG was much stronger in tension than GC. In ballistic tests, the BSG was the superior armor.
Improved Bar Impact Tests Using A Photonic Doppler Velocimeter
(2009-12) Bless, S. J.; Tolman, J.; Levinson, S.; Nguyen, J.; Bless, S. J.; Tolman, J.; Levinson, S.
Bar impact tests, using the techniques described elsewhere in this symposium, were used to measure compressive and tensile strengths of borosilicate glass, soda lime glass, and a glass ceramic. The glass ceramic was 25% crystalline spinel, furnished by Corning Inc. There are two measures of compressive strength: the peak stress that can be transmitted in unconfined compression, and the >steady state> strength. For borosilicate glass and soda lime glass, these values were similar, being about 1.8 and 1.5 GPa, respectively. The glass ceramic (25% spinel) was almost 50% stronger. Tensile failure in the glass and glass ceramic takes places via surface flaws, and thus tensile strength is an extrinsic, as opposed to intrinsic property.
Laser-Induced Spall Of Aluminum And Aluminum Alloys At High Strain Rates
(2007-12) Dalton, D. A.; Brewer, J.; Bernstein, A. C.; Grigsby, W.; Milathianaki, D.; Jackson, E.; Adams, R.; Rambo, P.; Schwarz, J.; Edens, A.; Geissel, M.; Smith, I.; Taleff, E.; Ditmire, T.; Dalton, D. A.; Brewer, J.; Bernstein, A. C.; Grigsby, W.; Milathianaki, D.; Jackson, E.; Taleff, E.; Ditmire, T.
We conducted laser-induced spall experiments aimed at studying how a material's microstructure affects the tensile fracture characteristics at high strain rates (> 10(6) s(-1)). We used the Z-Beamlet Laser at Sandia National Laboratory to drive shocks and to measure the spall strength of aluminum targets with various microstructures. The targets were recrystallized, high-purity aluminum (Al-HP RX), recrystallized aluminum + 3 wt.% magnesium (Al-3Mg RX), and cold-worked aluminum + 3 wt.% magnesium (Al-3Mg CW). The Al-3Mg RX and Al-3Mg CW are used to explore the roles that solid-solution alloying and cold-work strengthening play in the spall process. Using a line-VISAR (Velocity Interferometer System for Any Reflector) and analysis of recovered samples, we were able to measure spall strength and determine failure morphology in these targets. We find that the spall strength is highest for Al-HP RX. Analysis reveals that material grain size plays a vital role in the fracture morphology and spall strength results.
Numerical Simulation Of Impact Effects On Multilayer Fabrics
(2007-12) Fahrenthold, E.; Rabb, R.; Bohannan, A.; Fahrenthold, E.; Rabb, R.; Bohannan, A.
High strength fabrics provide lightweight impact protection and are employed in a wide range of applications. Examples include body armor for law enforcement and military personnel and orbital debris shielding for the International Space Station. Numerical simulation of impact effects on fabric protection systems is difficult., due to the complex woven structure of the fabric layers and the typical application of fabrics in a multilayer configuration. Recent research has applied a new particle-element method to the simulation of impact effects on multilayer fabrics, applicable over a wide range of impact velocities, for use in body armor and orbital debris shielding design applications.
Rotational Invariance, The Spin-Statistics Connection And The TCP Theorem
(2000-11) Sudarshan, E. C. G.; Sudarshan, E. C. G.
Quantum Field Theory formulated in terms of hermitian fields automatically leads to a spin-statistics connection when invariance under rotations is required. In three (or more) dimensions of space this implies Bose statistics for integer spin fields and Fermi statistics for half-integer spin fields. One should recall that spin-1/2 fields in three dimensions have two nonhermitian or four hermitian components. This automatic doubling of the number of components enables one to define a pseudoscalar matrix, and this in turn allows one to prove the TCP theorem for rotationally invariant field theories. In two space dimensions one obtains anyon statistics independent of the >spin>. For the quantum mechanics of identical particles we obtain only the possibility of either statistics for either spin as long as the spatial dimension is three (or highs). For two space dimensions we get anyon statistics. This difference is due to the contractibility of closed loops in three or more dimensions. The relation to the arguments of Broyles, of Bacry and of Berry and Robbins is discussed.
Sand Penetration By High-Speed Projectiles
(2009-12) Bless, S. J.; Berry, D. T.; Pedersen, B.; Lawhorn, W.; Bless, S. J.; Berry, D. T.; Pedersen, B.; Lawhorn, W.
Tungsten projectiles were shot into sand at velocities between 600 and 2200 m/s. Penetration was maximum at about 775 m/s. Below that velocity, projectiles were apparently stabilized by a fin set. Above that velocity, projectiles were broken by transverse loads. High-speed penetration resulted in comminution of sand particles, reducing their size by about 1000 times.
Spall And Dynamic Yielding Of Aluminum And Aluminum Alloys At Strain Rates Of 3X10(6) S(-1)
(2009-12) Dalton, D. A.; Worthington, D. L.; Sherek, P. A.; Pedrazas, N. A.; Bernstein, A. C.; Quevedo, H. J.; Rambo, P.; Schwarz, J.; Edens, A.; Geissel, M.; Smith, I. C.; Taleff, E. M.; Ditmire, T.; Dalton, D. A.; Worthington, D. L.; Sherek, P. A.; Pedrazas, N. A.; Bernstein, A. C.; Quevedo, H. J.; Taleff, E. M.; Ditmire, T.
We have explored the role that grain size, impurity particles and alloying in aluminum play in dynamic yielding and spall fracture at tensile strain rates of similar to 3x10(6) We achieved these strain rates shocking the aluminum specimens via laser ablation using the Z-Beamlet Laser at Sandia National Laboratories. The high purity aluminum and 1100 series aluminum alloy produced very different spall strengths and nearly the same yield strengths. In contrast, various grain-sized Al + 3 wt. % Mg specimens presented the lowest spall strength, but the greatest dynamic yield strength. Fracture morphology results and particle analysis are presented along with hydrodynamic simulations to put these results in context. Impurity particles appeared to play a vital role in spall fracture at these fast strain rates. Alloying elements such as Mg seem to be the dominant factor in the dynamic yield results.
Sporicidal Effects Of Iodine-Oxide Thermite Reaction Products
(2012-03) Russell, R.; Bless, S.; Blinkova, A.; Chen, Tiffany; Russell, R.; Bless, S.; Blinkova, A.; Chen, Tiffany
Iodine pentoxide-aluminum thermite reactions have been driven by impacts at 1000 m/s on steel plates 3 mm or thicker. This reaction releases iodine gas that is known to be a sporicide. To test the impact reactions for sporicidal effects, reactions took place in closed chambers containing dried Bacillus subtilis spores. The reduction in colony-forming units was dependent on the exposure time; long exposure times resulted in a 10(5) decrease in germination rate. This was shown to be due to the gas exposure rather than the heat or turbulence. Sporicidal effectiveness was increased by adding neodymium and saran resin.
X-Ray Tomography To Measure Size Of Fragments From Penetration Of High-Velocity Tungsten Rods
(2012-03) Stone, Z.; Bless, S.; Tolman, J.; McDonald, J.; Levinson, S.; Hanna, R.; Stone, Z.; Bless, S.; Tolman, J.; McDonald, J.; Levinson, S.; Hanna, R.
Behind-armor debris that results from tungsten rods penetrating armor steel at 2 km/s was studied by analysis of recovered fragments. Fragment recovery was by means of particle board. Individual fragments were analyzed by x-ray tomography, which provides information for fragment identification, mass, shape, and penetration down to masses of a few milligrams. The experiments were complemented by AUTODYN and EPIC calculations. Fragments were steel or tungsten generated from the channel or from the breakout through the target rear surface. Channel fragment motions were well described by Tate theory. Breakout fragments had velocities from the projectile remnant to the channel velocity, apparently depending on where in the projectile a fragment originated. The fragment size distribution was extremely broad and did not correlate well with simple uniform-fragment-size models.