Experimental realization of crossover in shape and director field of nematic tactoids
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Jamali, Vida↗
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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.
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Fusion and Fission Energy and Science Directorate and Information Technology Services Directorate HPC Cluster Reduction, Consolidation, and Savings in Data Center Space, Power, and Cooling
This report evaluates the benefits of decommissioning six legacy FFESD purchased HPC clusters and consolidating services and workloads into a new HPC cluster named HELIOS. The findings demonstrate significant reductions in the data center power and cooling requirements, data center footprint, and operational overhead, while simultaneously increasing computational capacity.
97 MATHEMATICS AND COMPUTING↗
Nematic director reorientation at solid and liquid interfaces under flow: SAXS studies in a microfluidic device
In this work we investigate the interplay between flow and boundary condition effects on the orientation field of a thermotropic nematic liquid crystal under flow and confinement in a microfluidic device. Two types of experiments were performed using synchrotron small-angle X-ray-scattering (SAXS). In the first, a nematic liquid crystal flows through a square-channel cross section at varying flow rates, while the nematic director orientation projected onto the velocity/velocity gradient plane is measured using a 2D detector. At moderate-to-high flow rates, the nematic director is predominantly aligned in the flow direction, but with a small tilt angle of ~±11° in the velocity gradient direction. The director tilt angle is constant throughout most of the channel width but switches sign when crossing the center of the channel, in agreement with the Ericksen–Leslie–Parodi (ELP) theory. At low flow rates, boundary conditions begin to dominate, and a flow profile resembling the escaped radial director configuration is observed, where the director is seen to vary more smoothly from the edges (with homeotropic alignment) to the center of the channel. In the second experiment, hydrodynamic focusing is employed to confine the nematic phase into a sheet of liquid sandwiched between two layers of Triton X-100 aqueous solutions. The average nematic director orientation shifts to some extent from the flow direction toward the liquid boundaries, although it remains unclear if one tilt angle is dominant through most of the nematic sheet (with abrupt jumps near the boundaries) or if the tilt angle varies smoothly between two extreme values (~90 and 0°). Lastly, the technique presented here could be applied to perform high-throughput measurements for assessing the influence of different surfactants on the orientation of nematic phases and may lead to further improvements in areas such as boundary lubrication and clarifying the nature of defect structures in LC displays.
36 MATERIALS SCIENCE↗
Phonon-induced rotation of the electronic nematic director in superconducting Bi 2 Se 3
The doped topological insulator A x Bi 2 Se 3 , with A = {Cu,Sr,Nb}, becomes a nematic superconductor below T c ≈ 3–4 K. The associated electronic nematic director is described by an angle α and is experimentally manifested in the elliptical shape of the in-plane critical magnetic field H c2 . Because of the threefold rotational symmetry of the lattice, α is expected to align with one of three high-symmetry directions corresponding to the in-plane nearest-neighbor bonds, consistent with a Z 3 -Potts nematic transition. Here, we show that the nematic coupling to the acoustic phonons, which makes the nematic correlation length tend to diverge along certain directions only, can fundamentally alter this phenomenology in trigonal lattices. Compared to hexagonal lattices, the former possesses a sixth independent elastic constant c14 due to the fact that the in-plane shear strain doublet (ε xx – ε yy , – 2ε xy ) and the out-of-plane shear strain doublet (2ε yz , – 2ε zx ) transform as the same irreducible representation. We find that, when c 14 overcomes a threshold value, which is expected to be the case in doped Bi 2 Se 3 , the nematic director α unlocks from the high-symmetry directions due to the competition between the quadratic phonon-mediated interaction and the cubic nematic anharmonicity. This implies the breaking of the residual in-plane twofold rotational symmetry (C 2x ), resulting in a triclinic phase. Furthermore, we discuss the implications of these findings for the structure of nematic domains, for the shape of the in-plane H c2 in A x Bi 2 Se 3 , and for the presence of nodes inside the superconducting state.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Effect of an electric field on the orientation of a liquid crystal in a cell with a nonuniform director distribution
The electric field-induced reorientation of a nematic liquid crystal in cells with a planar helicoidal or a homeoplanar structure of a director field is studied theoretically and experimentally. The dependences of the capacitances of these systems on the voltage in an applied electric field below and above the Fréedericksz threshold are experimentally obtained and numerically calculated. The calculations use the director distribution in volume that is obtained by direct minimization of free energy at various voltages. The inhomogeneity of the electric field inside a cell is taken into account. The calculation results are shown to agree with the experimental data.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Surface Anchoring and Director Distribution in a Grandjean–Cano Wedge
Theoretical calculations of the director distribution in a Grandjean–Cano wedge in relation to the anchoring strength and mutual orientation of the easy axes at the wedge surfaces are performed for various model surface anchoring potentials. Comparison of the theory and experiment allows one to propose the socalled model D-potential, quadratic in angle of director deviation from the easy axes, as the best one in fitting the experiment in the angular range of performed measurements. To satisfy general requirements on the wedge surface, a modified D-potential is proposed. The optimal conditions of the experiment aimed at restoring the potential in the whole range of its definition (in particular, nonparallel orientation of the easy axes at the wedge surfaces) are formulated.
71 CLASSICAL AND QUANTUM MECHANICS, GENERAL PHYSIC↗
Director and Spontaneous Polarization Fluctuations in Ferroelectric Smectic-C* Cells
The correlation function of the director fluctuations in a plane-parallel smectic-C* cell with a bookshelf structure is calculated far from phase transition points. The free energy takes into account the anisotropy of the Coulomb interaction of the bound charges induced by spontaneous polarization fluctuations. This correlation function of the director fluctuations is used to calculate the scattered light intensity. Taking into account the anisotropy of the permittivity in the Coulomb interaction of bound charges is shown to change a scattering indicatrix substantially.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Associate Laboratory Directorate for Weapon Physics (ALDX) [Slides]
ALDX is one of seven technical Directorates at the Laboratory and resides within the Weapons Program. The Weapons Physics Directorate stewards a number of critical capabilities to meet its mission. Our mission is to sustain the resilience of the US nuclear stockpile and help shape a globalized nuclear world. Sustaining the aging stockpile poses scientific challenges to assess and certify the stockpile without testing. We are helping to solve major technical challenges in the nuclear global security regime. Geopolitical realities demand the Laboratory’s excellence in providing solutions to national security problems. High Performance Computing at Los Alamos opens the doors to many sophisticated modeling techniques. We use many experimental facilities to probe weapons physics. The diverse skill set required to execute ALDX’s mission has benefited greatly from the Postdoc program.
45 MILITARY TECHNOLOGY, WEAPONRY, AND NATIONAL DEF↗
Did you know the Lab and its first director share a birthday month? A look back at Oppenheimer’s wartime legacy through historical items in our collections
Many birthdays ago, at only 38 years old and with no previous administrative experience, J. Robert Oppenheimer accepted responsibility for a national security mission of unprecedented scale. His charge, handed down by Manhattan Project director General Leslie R. Groves, was to lead a team of the world’s foremost scientific minds in developing the first atomic bomb. Under Oppenheimer’s leadership, a community of over 6,000 scientists, engineers, and other personnel living and working at the top-secret lab in Los Alamos completed their task in only 27 months, delivering the world’s first two atomic weapons to the U.S. military. In honor of what would have been Oppenheimer’s 119th birthday (on April 22), the National Security Research Center remembers his contributions as an administrator and scientist and the scope of his legacy as the first director of the Lab through items in our unclassified collections.
99 GENERAL AND MISCELLANEOUS↗
Attend debut of new film on the Lab’s first director
The NSRC’s much-anticipated documentary, Oppenheimer: Science, Mission, Legacy, will premiere for Lab staff later this summer at the NSSB auditorium, and then be made available online. Speakers at the premiere will include film creator and primary producer Dave Tietmeyer (Multimedia Services, CEA-MP), Senior Historian Alan Carr (WRS-NSCMS), and NSRC Director Brye Steeves (WRS-DO). The film was entirely produced by the NSRC and Laboratory staff and will commemorate former director J. Robert Oppenheimer and his endeavors. Much of the material and several scenes featured in the film are based on collections from the Manhattan Project era and interviews with today’s Lab staff and Oppenheimer experts.
99 GENERAL AND MISCELLANEOUS↗
Watch it again-or for the first time: Panel discussion and Q&A on First Lab Director J. Robert Oppenheimer
On June 19, 2023, at the National Security Sciences Building (NSSB) auditorium, LANL Director Thom Mason, LANL physicist Anna Llobet, American Prometheus author Kai Bird, and retired Senate staff member Tim Rieser discussed the life, work and legacy of first Lab Director J. Robert Oppenheimer. The panel event was moderated by LANL senior historian Alan Carr.
99 GENERAL AND MISCELLANEOUS↗
A Profile of Academic Training Program Directors and Chairs in Radiation Oncology
Purpose: To identify objective characteristics and benchmarks for program leadership in academic radiation oncology. Methods and Materials: A study of the 87 Accreditation Council for Graduate Medical Education radiation oncology training program directors (PD) and their chairs was performed. Variables included age, gender, original training department, highest degree, rank, endowed chair assignment, National Institutes of Health (NIH) funding, and Hirsch index (H-index). Data were gathered from online sources such as departmental websites, NIH RePORTER, and Scopus. Results: There were a total of 87 PD. The median age was 48, and 14 (16%) were MD/PhD. A total of 21 (24%) were female, and rank was relatively equally distributed above instructor. Of the 26 professors, at least 7 (27%) were female. At least 24 (28%) were working at the institution from which they had received their training. A total of 6 individuals held endowed chairs. Only 2 PD had active NIH funding in 2012. The median H-index was 12 (range, 0-51) but the index dropped to 9 (range, 0-38) when those who served as both PD and chair were removed from the group. A total of 76 chairs were identified at the time of the study. The median age was 55, and 9 (12%) were MD/PhD. A total of 7 (9%) of the chairs were female, and rank was professor for all with the exception of 1 who was listed as “Head” and was an associate professor. Of the 76 chairs, at least 10 (13%) were working at the institution from which they received their training. There were a total of 21 individuals with endowed chairs. A total of 13 (17%) had NIH funding in 2012. The median H-index was 29 (range, 3-60). Conclusions: These data provide benchmarks for individuals and departments evaluating leadership positions in the field of academic radiation oncology. Such data are useful for evaluating leadership trends over time and comparing academic radiation oncology with other specialties.
62 RADIOLOGY AND NUCLEAR MEDICINE↗
Stress and Burnout Among Residency Program Directors in United States Radiation Oncology Programs
Purpose: To evaluate stressors among radiation oncology residency program directors (PDs) and determine the prevalence and indicators of burnout. Methods and Materials: An anonymous, online, cross-sectional survey was offered to PDs of US radiation oncology programs in the fall of 2014. Survey content examined individual and program demographics, perceptions surrounding the role of PD, and commonly encountered stressors. Burnout was assessed using the validated Maslach Burnout Inventory-Human Services Survey. Results: In total, 47 of 88 PDs (53%) responded to the survey. Although 78% of respondents reported feeling “satisfied” or “highly satisfied” with their current role, 85% planned to remain as PD for <5 years. The most commonly cited stressors were satisfying Accreditation Council for Graduate Medical Education/Residency Review Committee requirements (47%), administrative duties (30%) and resident morale (28%). Three-quarters of respondents were satisfied that they became PDs. Overall, 11% of respondents met criteria for low burnout, 83% for moderate burnout, and 6% for high burnout. Not having served as a PD at a prior institution correlated with high depersonalization (OR 6.75, P=.04) and overall burnout (odds ratio [OR], 15.6; P=.04). Having more years on faculty prior to becoming PD correlated with less emotional exhaustion (OR, 0.44, P=.05) and depersonalization (OR, 0.20, P=.04). Finally, having dedicated time for PD duties correlated with less emotional exhaustion (OR, 0.27, P=.04). Conclusions: Moderate levels of burnout are common in U.S. radiation oncology PDs with regulatory stressors being common. Despite this, many PDs are fulfilled with their role. Longitudinal studies assessing dynamic external factors and their influence on PD burnout would be beneficial.
62 RADIOLOGY AND NUCLEAR MEDICINE↗
A machine learning approach to robustly determine director fields and analyze defects in active nematics
A machine learning model for reliable director fields calculation from raw experimental images of active nematics. The model is accurate, robust to noise and generalizable, enhancing analysis such as the detection and tracking of topological defects.
97 MATHEMATICS AND COMPUTING↗
Technical Review of the Domestic Nuclear Detection Office Transformational and Applied Research Directorate’s Research and Development Program
At the request of the Domestic Nuclear Detection Office (DNDO), a Review Committee comprised of representatives from the American Physical Society (APS) Panel on Public Affairs (POPA) and the Institute of Electrical and Electronics Engineers (IEEE) Nuclear and Plasma Sciences Society (NPSS) performed a technical review of the DNDO Transformational and Applied Research Directorate (TARD) research and development program. TARD’s principal objective is to address gaps in the Global Nuclear Detection Architecture (GNDA) through improvements in the performance, cost, and operational burden of detectors and systems. The charge to the Review Committee was to investigate the existing TARD research and development plan and portfolio, recommend changes to the existing plan, and recommend possible new R&D areas and opportunities. The Review Committee has several recommendations.
detectors, detection algorithms, strategic plannin↗
Energy exchange between electromagnetic waves on the director diffraction grating in planar waveguide with nematic layer
The energy exchange between two coupled TE modes on the diffraction grating of the director in a planar waveguide containing a nematic liquid crystal layer is calculated. The diffraction grating is induced by an external electric field in the nematic layer with periodic anchoring energy at the waveguide surface. The intensity of the signal mode at the output of the nematic layer is calculated as a function of the amplitude and period of the anchoring-energy modulation, the nematic layer sizes, and the electric-field strength. The cases of modes with the same and opposite directions are considered. Analytical expressions for the maximum intensities of the signal mode are derived. In both cases the maximum intensity of the signal mode increases with an increase in the electric-field strength.
75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗
Global Security Input for Director's All Employee Meeting
This report provides a slideshow presentation on the Global Security Input for Director's All Employee Meeting.
98 NUCLEAR DISARMAMENT, SAFEGUARDS, AND PHYSICAL P↗
External Review Committee Report, Physical and Life Sciences Directorate 2018
The committee was charged with reviewing the health of the Nuclear and Chemical Sciences Division (NACS) and its impact on LLNL and national security. Overarching observations and recommendations are given here, with detailed comments in the body of the report. NACS was formed in 2014 with the goal of growing a coordinated nuclear physics and chemistry portfolio. Evidence from the talks, posters, tour, and discussions with employees indicated that the division is performing remarkably well. The basis for this comes from world-class science coupled with programmatic needs, the ability to hire and retain the best and the brightest, and a work force with high morale. The planning exercises and production of strategic vision documents to achieve these goals is particularly impressive. The directorate and division management should be congratulated.
42 ENGINEERING↗