2,589 research outputs found
Detection of electronic excited states in conjugated polymers by picosecond transient strain spectroscopy
Journal ArticleWe describe a new type of spectroscopy based on picosecond transient strain in absorption photomodulation that can be used to detect and identify both allowed and forbidden optical transitions in solid thin films. We have applied the new spectroscopy to a variety of conducting polymer films such as polythiophene, trans and cis polyacetylene, and poly(diethynyl-silane), in which we measured energy levels of various excitonic states with odd and even symmetry that are, respectively, allowed and forbidden in the optical absorption
Validating gravitational-wave detections: The Advanced LIGO hardware injection system
Hardware injections are simulated gravitational-wave signals added to the Laser Interferometer Gravitational-wave Observatory (LIGO). The detectors’ test masses are physically displaced by an actuator in order to simulate the effects of a gravitational wave. The simulated signal initiates a control-system response which mimics that of a true gravitational wave. This provides an end-to-end test of LIGO’s ability to observe gravitational waves. The gravitational-wave analyses used to detect and characterize signals are exercised with hardware injections. By looking for discrepancies between the injected and recovered signals, we are able to characterize the performance of analyses and the coupling of instrumental subsystems to the detectors’ output channels. This paper describes the hardware injection system and the recovery of injected signals representing binary black hole mergers, a stochastic gravitational wave background, spinning neutron stars, and sine-Gaussians
Phase Diagram for Charge Density Waves in a Magnetic Field
The influence of an external magnetic field on a quasi one-dimensional system
with a charge density wave (CDW) instability is treated within the random phase
approximation which includes both CDW and spin density wave correlations. We
show that the CDW is sensitive to both orbital and Pauli effects of the field.
In the case of perfect nesting, the critical temperature decreases monotonously
with the field, and the wave vector of the instability starts to shift above
some critical value of magnetic field. Depending on the ratio between the spin
and charge coupling constants and on the direction of the applied magnetic
field, the wave vector shift is either parallel ( order) or
perpendicular ( order) to the most conducting direction. The
order is a field dependent linear combination of the charge and spin density
waves and is sensible only to the Pauli effect. The wave vector shift in
depends on the interchain coupling, but the critical temperature does
not. This order is affected by the confinement of the electronic orbits. By
increasing the relative strength of the orbital effect with respect to the
Pauli effect, one can destroy the , establishing either a , or a
(corresponding to perfect nesting wave vector). We also show that by
increasing the imperfect nesting parameter, one passes from the regime where
the critical temperature decreases with the field to the regime where it is
initially enhanced by the orbital effect and eventually suppressed by the Pauli
effect. For a bad nesting, the quantized phases of the field-induced CDW
appear.Comment: 30 pages (LaTeX) + 15 figure
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The effects of 800 MeV proton irradiation on the corrosion of tungsten, tantalum, stainless steel, and gold
Real time electrochemical data were acquired for tungsten, tantalum, stainless steel 304L, and gold targets during proton irradiation at the LANSCE Weapons Neutron Research Facility. The goal of this research was to establish a better understanding of the corrosion properties of materials as a function of proton irradiation and gain insight into the mechanism of the observed phenomena. The following electrochemical observations were made during proton irradiation of W, Ta, SS304, and Au: (1) the open circuit potential of all materials increased with increasing proton fluence; (2) the corrosion rate (at the OCP) of W and SS304 increased with increasing proton fluence; (3) the passive dissolution rate for SS304 and Ta decreased with increasing proton fluence; (4) the anodic dissolution rate for W increased with increasing proton fluence; (5) the pitting potential for SS304 increased with proton fluence, which is an indication that the material is less susceptible to pitting attack during irradiation
A List of Galaxies for Gravitational Wave Searches
We present a list of galaxies within 100 Mpc, which we call the Gravitational
Wave Galaxy Catalogue (GWGC), that is currently being used in follow-up
searches of electromagnetic counterparts from gravitational wave searches. Due
to the time constraints of rapid follow-up, a locally available catalogue of
reduced, homogenized data is required. To achieve this we used four existing
catalogues: an updated version of the Tully Nearby Galaxy Catalog, the Catalog
of Neighboring Galaxies, the V8k catalogue and HyperLEDA. The GWGC contains
information on sky position, distance, blue magnitude, major and minor
diameters, position angle, and galaxy type for 53,255 galaxies. Errors on these
quantities are either taken directly from the literature or estimated based on
our understanding of the uncertainties associated with the measurement method.
By using the PGC numbering system developed for HyperLEDA, the catalogue has a
reduced level of degeneracies compared to catalogues with a similar purpose and
is easily updated. We also include 150 Milky Way globular clusters. Finally, we
compare the GWGC to previously used catalogues, and find the GWGC to be more
complete within 100 Mpc due to our use of more up-to-date input catalogues and
the fact that we have not made a blue luminosity cut.Comment: Accepted for publication in Classical and Quantum Gravity, 13 pages,
7 figure
Some Notable Discoveries in Organosilicon Chemistry: Proceedings of the History and Retrospective Session of the 34th Organosilicon Symposium (2001)
The 34th Organosilicon Symposium at White Plains, NY, in 2001 featured a History and Retrospective Session, during which invited speakers from academic and industrial laboratories recounted the path to some significant 20th century discoveries in organosilicon chemistry. The Si=C Story: The Way it Happened, Adrian G. Brook (University of Toronto) The Discovery of Stable Disilenes and Silylenes, Robert West (University of Wisconsin) Yellow Fever: The Story Behind the Synthesis of Germasilenes, Kim M. Baines (University of Western Ontario) Direct Synthesis of Tris(dimethylamino)silane, William B. Herdle (OSi Specialties, formerly of Union Carbide Corporation) Discovery of Tin and Phosphorus Effects on the Direct Synthesis of Methylchlorosilanes, Larry H. Wood (Dow Corning Corporation) Discovery of Methylchlorosilylene (CH3SiCl) as a Key Intermediate in the Direct Synthesis of Dimethyldichlorosilane ((CH3)2SiCl2), Kenrick M. Lewis (OSi Specialties, formerly of Union Carbide Corporation) The First Platinum-Catalyzed Hydrosilylation With Supported Platinum Catalysts, George H. Wagner (Retired, formerly of Union Carbide Corporation) The Discovery of Silicone Surfactants for Polyurethane Foam, Bernard Kanner (Retired, formerly of Union Carbide Corporation) The Discovery of Silane Coupling Agents, Bernard Kanner (Retired, formerly of Union Carbide Corporation)https://ir.lib.uwo.ca/organosiliconproceedings/1006/thumbnail.jp
Pressure Tuning of the Charge Density Wave in the Halogen-Bridged Transition-Metal (MX) Solid
We report the pressure dependence up to 95 kbar of Raman active stretching
modes in the quasi-one-dimensional MX chain solid . The data
indicate that a predicted pressure-induced insulator-to-metal transition does
not occur, but are consistent with the solid undergoing either a
three-dimensional structural distortion, or a transition from a charge-density
wave to another broken-symmetry ground state. We show that such a transition
cacan be well-modeled within a Peierls-Hubbard Hamiltonian. 1993 PACS:
71.30.+h, 71.45.Lr, 75.30.Fv, 78.30.-j, 81.40.VwComment: 4 pages, ReVTeX 3.0, figures available from the authors on request
(Gary Kanner, [email protected]), to be published in Phys Rev B Rapid
Commun, REVISION: minor typos corrected, LA-UR-94-246
Using ISS Telescopes for Electromagnetic Follow-up of Gravitational Wave Detections of NS-NS and NS-BH Mergers
The International Space Station offers a unique platform for rapid and inexpensive deployment of space telescopes. A scientific opportunity of great potential later this decade is the use of telescopes for the electromagnetic follow-up of ground-based gravitational wave detections of neutron star and black hole mergers. We describe this possibility for OpTIIX, an ISS technology demonstration of a 1.5 m diffraction limited optical telescope assembled in space, and ISS-Lobster, a wide-field imaging X-ray telescope now under study as a potential NASA mission. Both telescopes will be mounted on pointing platforms, allowing rapid positioning to the source of a gravitational wave event. Electromagnetic follow-up rates of several per year appear likely, offering a wealth of complementary science on the mergers of black holes and neutron stars
2014 Epilepsy Benchmarks Area III: Improve Treatment Options for Controlling Seizures and Epilepsy-Related Conditions Without Side Effects
The Epilepsy Benchmark goals in Area III focus on making progress in understanding and controlling seizures and related conditions as well as on developing biomarkers and new therapies that will reduce seizures and improve outcomes for individuals with epilepsy. Area III emphasizes a need to better understand the ways in which seizures start, propagate, and terminate and whether those network processes are common or unique in different forms of epilepsy. The application of that knowledge to improved seizure prediction and detection will also play a role in improving patient outcomes. Animal models of treatment-resistant epilepsy that are aligned with etiologies and clinical features of human epilepsies are especially encouraged as necessary tools to understand mechanisms and test potential therapies. Antiseizure therapies that target (either alone or in combination) novel or multiple seizure mechanisms are prioritized in this section of the Benchmarks. Area III goals also highlight validation of biomarkers of treatment response and safety risk, effective self-management, and patient-centered outcome measures as important areas of emphasis for the next five to ten years
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