Los Alamos National Laboratory is one of two laboratories in the United States where classified work towards the design of nuclear weapons is undertaken. The other, since 1952, is Lawrence Livermore National Laboratory. LANL is a United States Department of Energy national laboratory, managed and operated by Los Alamos National Security , located in Los Alamos, New Mexico. The laboratory is one of the largest science and technology institutions in the world. It conducts multidisciplinary research in fields such as national security, space exploration, renewable energy, medicine, nanotechnology, and supercomputing.LANL is the largest institution and the largest employer in northern New Mexico, with approximately 9,000 direct employees and around 650 contractor personnel. Additionally, there are roughly 120 DOE employees stationed at the laboratory to provide federal oversight of LANL's work and operations. Approximately one-third of the laboratory's technical staff members are physicists, one quarter are engineers, one-sixth are chemists and materials scientists, and the remainder work in mathematics and computational science, biology, geoscience, and other disciplines. Professional scientists and students also come to Los Alamos as visitors to participate in scientific projects. The staff collaborates with universities and industry in both basic and applied research to develop resources for the future. The annual budget is approximately US$2.2 billion. Wikipedia.
Elliott S.R.,Los Alamos National Laboratory |
Franz M.,University of British Columbia
Reviews of Modern Physics | Year: 2015
Ettore Majorana (1906-1938) disappeared while traveling by ship from Palermo to Naples in 1938. His fate has never been fully resolved and several articles have been written that explore the mystery itself. His demise intrigues us still today because of his seminal work, published the previous year, that established symmetric solutions to the Dirac equation that describe a fermionic particle that is its own antiparticle. This work has long had a significant impact in neutrino physics, where this fundamental question regarding the particle remains unanswered. But the formalism he developed has found many uses as there are now a number of candidate spin-1/2 neutral particles that may be truly neutral with no quantum number to distinguish them from their antiparticles. If such particles exist, they will influence many areas of nuclear and particle physics. Most notably the process of neutrinoless double beta decay can exist only if neutrinos are massive Majorana particles. Hence, many efforts to search for this process are underway. Majorana's influence does not stop with particle physics, however, even though that was his original consideration. The equations he derived also arise in solid-state physics where they describe electronic states in materials with superconducting order. Of special interest here is the class of solutions of the Majorana equation in one and two spatial dimensions at exactly zero energy. These Majorana zero modes are endowed with some remarkable physical properties that may lead to advances in quantum computing and, in fact, there is evidence that they have been experimentally observed. This Colloquium first summarizes the basics of Majorana's theory and its implications. It then provides an overview of the rich experimental programs trying to find a fermion that is its own antiparticle in nuclear, particle, and solid-state physics. © 2015 American Physical Society.
Beresnyak A.,Los Alamos National Laboratory
Physical Review Letters | Year: 2011
The spectral slope of strong MHD turbulence has recently been a matter of controversy. While the Goldreich-Sridhar model predicts a -5/3 slope, shallower slopes have been observed in numerics. We argue that earlier numerics were affected by driving due to a diffuse locality of energy transfer. Our highest-resolution simulation (30722×1024) exhibited the asymptotic -5/3 scaling. We also discover that the dynamic alignment, proposed in models with -3/2 slope, saturates and cannot modify the asymptotic, high Reynolds number slope. From the observed -5/3 scaling we measure the Kolmogorov constant C KA=3.27±0.07 for Alfvénic turbulence and C K=4.2±0.2 for full MHD turbulence, which is higher than the hydrodynamic value of 1.64. This larger CK indicates inefficient energy transfer in MHD turbulence, which is in agreement with diffuse locality. © 2011 American Physical Society.
Del Campo A.,Los Alamos National Laboratory
Physical Review Letters | Year: 2013
The evolution of a system induced by counterdiabatic driving mimics the adiabatic dynamics without the requirement of slow driving. Engineering it involves diagonalizing the instantaneous Hamiltonian of the system and results in the need of auxiliary nonlocal interactions for matter waves. Here, experimentally realizable driving protocols are found for a large class of single-particle, many-body, and nonlinear systems without demanding the spectral properties as an input. The method is applied to the fast decompression of Bose-Einstein condensates in different trapping potentials. © 2013 American Physical Society.
Shoemaker I.M.,Los Alamos National Laboratory
Physics of the Dark Universe | Year: 2013
The mass of primordial dark matter (DM) protohalos remains unknown. However, the missing satellites problem may be an indication that they are quite large. In this paper, we use effective field theory to map constraints on dark matter-SM interactions into limits on the mass of DM protohalos. Given that leptons remain in the thermal bath until late times, we focus on their interactions with DM. To illustrate the method, we use the null results of LEP missing energy searches along with Fermi-LAT searches for DM annihilation in nearby dwarf galaxies, to derive limits on the protohalo mass, ≲ (10-6 to 10-1)M⊙, with the range depending on the DM mass and the operator. Thus, if DM is to remain thermally coupled until late times and account for the missing satellites, charged lepton interactions are insufficient. This motivates neutrinophilic DM, which can have protohalo masses orders of magnitude larger, with constraints arising from Planck, IceCube and unpublished Super-K data. We show that effective neutrinophilic models offer a viable solution to the missing satellites problem for sub-GeV DM masses with larger than WIMP-sized annihilation cross sections. © 2013 Ian M. Shoemaker.
Jones M.B.,Los Alamos National Laboratory |
Gaunt A.J.,Los Alamos National Laboratory
Chemical Reviews | Year: 2013
A study was conducted to report the latest developments in synthesis and structural chemistry of nonaqueous actinide complexes. The term nonaqueous was defined to mean those molecules whose crystal structures did not contain water. The nonaqueous molecule was included when it was synthesized using hydrated solids as precursors, but the reaction chemistry was performed exclusively in an organic solvent. All of the actinides were found to be radioactive and synthetic scale experiments were performed with appropriate analyses of hazards and implementation of controls and safety procedures concerning actinide radioisotopes.
Sanbonmatsu K.Y.,Los Alamos National Laboratory
Current Opinion in Structural Biology | Year: 2012
The past decade has produced an avalanche of experimental data on the structure and dynamics of the ribosome. Groundbreaking studies in structural biology and kinetics have placed important constraints on ribosome structural dynamics. However, a gulf remains between static structures and time dependent data. In particular, X-ray crystallography and cryo-EM studies produce static models of the ribosome in various states, but lack dynamic information. Single molecule studies produce information on the rates of transitions between these states but do not have high-resolution spatial information. Computational studies have aided in bridging this gap by providing atomic resolution simulations of structural fluctuations and transitions between configurations. © 2012.
Rusty Gray III G.T.,Los Alamos National Laboratory
Annual Review of Materials Research | Year: 2012
The influence of increasing strain rate on the mechanical behavior and deformation substructures in metals and alloys that deform predominately by slip is very similar to that seen following quasi-static deformation at increasingly lower temperatures or due to a decrease in stacking-fault energy (γsf). Deformation at higher rates (a) produces more uniform dislocation distributions for the same amount of strain, (b) hinders the formation of discrete dislocation cells, (c) decreases cell size, and (d) increases misorientation, with more dislocations trapped within cell interiors. The suppression of thermally activated dislocation processes in this regime can lead to stresses high enough to activate and grow deformation twins even in high-stacking-fault-energy, face-centered-cubic metals. In this review, examples of the high-strain-rate mechanical behavior and the deformation substructure evolution observed in a range of materials following high and shock-loading strain rates are presented and compared with those seen following quasi-static-loading deformation paths. © Copyright ©2012 by Annual Reviews. All rights reserved.
Klimov V.I.,Los Alamos National Laboratory
Annual Review of Condensed Matter Physics | Year: 2014
Chemically synthesized semiconductor nanocrystals (NCs) have been extensively studied as a test bed for exploring the physics of strong quantum confinement and as a highly flexible materials platform for the realization of a new generation of solution-processed optical, electronic, and optoelectronic devices. Because of readily tunable, size-dependent emission and absorption spectra, colloidal NCs are especially attractive for applications in light-emitting diodes, solid-state lighting, lasing, and solar cells. It is universally recognized that the realization of these and other prospective applications of NCs requires a detailed understanding of carrier-carrier interactions in these structures, as they have a strong effect on both recombination and photogeneration dynamics of charge carriers. For example, nonradiative Auger recombination is one of the key factors limiting the performance of NC-based lasers and light-emitting diodes. The inverse of this process, carrier multiplication, plays a beneficial role in light harvesting and can be used to boost the efficiency of photovoltaics through increased photocurrent. This article reviews recent progress in the understanding of multicarrier processes in NCs of various complexities, including zero-dimensional spherical quantum dots, quasi-one-dimensional nanorods, and various types of core-shell heterostructures. This review's specific focus is on recent efforts toward controlling multicarrier interactions using traditional approaches, such as size and shape control, as well as newly developed methods involving interface engineering for suppression of Auger decay and engineering of intraband cooling rates for enhancement of carrier multiplication. © Copyright 2014 by Annual Reviews. All rights reserved.
Chen H.-T.,Los Alamos National Laboratory
Optics Express | Year: 2012
The impedance matching to free space in metamaterial perfect absorbers has been believed to involve and rely on magnetic resonant response, with direct evidence provided by the anti-parallel surface currents in the metal structures. Here I present a different theoretical interpretation based on interference, which shows that the two layers of metal structures in metamaterial absorbers are linked only by multiple reflections with negligible near-field interactions or magnetic resonances. This is further supported by the out-of-phase surface currents derived at the interfaces of resonator array and ground plane through multiple reflections and superpositions. The theory developed here explains all features observed in narrowband metamaterial absorbers and therefore provides a profound understanding of the underlying physics. © 2012 Optical Society of America.
Wu G.,Los Alamos National Laboratory |
Zelenay P.,Los Alamos National Laboratory
Accounts of Chemical Research | Year: 2013
Platinum-based catalysts represent a state of the art in the electrocatalysis of oxygen reduction reaction (ORR) from the point of view of their activity and durability in harnessing the chemical energy via direct electrochemical conversion. However, because platinum is both expensive and scarce, its widespread implementation in such clean energy applications is limited. Recent breakthroughs in the synthesis of high-performance nonprecious metal catalysts (NPMCs) make replacement of Pt in ORR electrocatalysts with earth-abundant elements, such as Fe, Co, N, and C, a realistic possibility. In this Account, we discuss how we can obtain highly promising M-N-C (M: Fe and/or Co) catalysts by simultaneously heat-treating precursors of nitrogen, carbon, and transition metals at 800-1000 C. The activity and durability of resulting catalysts depend greatly on the selection of precursors and synthesis chemistry. In addition, they correlate quite well with the catalyst nanostructure. While chemists have presented no conclusive description of the active catalytic site for this class of NPMCs, they have developed a designed approach to making active and durable materials, focusing on the catalyst nanostructure. The approach consists of nitrogen doping, in situ carbon graphitization, and the usage of graphitic structures (possibly graphene and graphene oxides) as carbon precursors. Various forms of nitrogen, particularly pyridinic and quaternary, can act as n-type carbon dopants in the M-N-C catalysts, assisting in the formation of disordered carbon nanostructures and donating electrons to the carbon. The CNx structures are likely a crucial part of the ORR active site(s). Noteworthy, the ORR activity is not necessarily governed by the amount of nitrogen, but by how the nitrogen is incorporated into the nanostructures.Apart from the possibility of a direct participation in the active site, the transition metal often plays an important role in the in situ formation of various carbon nanostructures by catalyzing the decomposition of the nitrogen/carbon precursor. We can control the formation of different nanostructures during the synthesis of M-N-C catalysts. For example, in situ formed nitrogen-doped graphene-sheets can only be derived from polyaniline (PANI), probably due to structural similarities between the aromatic structures of PANI and graphene. Highly-graphitized carbon nanostructures may serve as a matrix for the formation of ORR-active groups with improved catalytic activity and durability, containing nitrogen and most probably also metal atoms. In the future, we will likely focus NPMC synthesis approaches on precise control of interactions between precursors of the metal and carbon/nitrogen during the heat treatment. The main purposes will be to maximize the number of active sites, optimize nitrogen doping levels, and generate morphologies capable of hosting active and stable ORR sites. © 2013 American Chemical Society.