Physics Commons^™

Review Of The Future Of U.S. Nuclear Weapons Policy, David W. Hafemeister

Physics

No abstract provided.

How Much Reliability And Yield Is Enough For A Ctbt?, David W. Hafemeister

Physics

No abstract provided.

Biomineralization Of Magnetic Iron Minerals In Bacteria, Richard B. Frankel, Dennis A. Bazylinski, Dirk Schϋler

Physics

Magnetotactic bacteria orient and migrate along magnetic field lines. This ability is based on a submicron assembly of single-magnetic domain iron mineral particles that elegantly solves the problem of how to construct a magnetic dipole that is large enough to be oriented in the geomagnetic field at ambient temperature, yet fit inside a micron-sized cell. The solution is based on the ability of the bacteria to accumulate high concentrations of iron, and control the deposition, size and orientation of a specific iron mineral at specific locations in the cell.

"Hands-On" Epicycles And Retrograde Motion, Matthew J. Moelter, Bernard A. Bates

Physics

No abstract provided.

Hands-On Phasors And Multiple-Slit Interference, Rand S. Worland, Matthew J. Moelter

Physics

No abstract provided.

Reaction Of Dioxygen With A Cross-Conjugated Carbon-Carbon Double Bond In A Bis-Macrocycle Diiron Compound, D. Brent Macqueen, Christopher Lange, Melvin Calvin, John W. Otvos, Larry O. Spreer, Christian B. Allan, Anna Ganse, Richard B. Frankel

Physics

Dioxygen at atmospheric pressure attacks a cross-conjugated carbon-carbon double bond in a diiron complex to form two, like, keto macrocyclic iron(II) complexes. This reaction occurs with high yield in both solution and in the solid state. A dioxetane intermediate is, therefore, invoked. The rate of the reaction is very dependent on the nature of the axial ligands on the low-spin iron(II) ions in the bimetallic complex. The rate is at least a factor of 10⁴ faster with DMF ligands than with CH₃CN axial ligands. This rate dependence is explained by stabilization of a peroxo biradical transition state …

Determination Of The Preexponential Frequency Factor For Superparamagnetic Maghemite Particles In Magnetoferritin, Bruce M. Moskowitz, Richard B. Frankel, Sarah A. Walton, Dominic P. E. Dickson, K. K. W. Wong, T. Douglas, Stephen Mann

Physics

Magnetization and Mössbauer measurements on maghemite particles with an average particle diameter of 10 nm have been made in the temperature range from 5 K to 353 K spanning the superparamagnetic (SPM) and stable single domain (SD) regimes. The maghemite particles were produced within the iron-storage protein ferritin, resulting in a narrowly-sized, weakly interacting nanocomposite material called magnetoferritin. Experiments combining hysteresis measurements, low temperature remanence, and Mössbauer spectroscopy were used to characterize magnetoferritin and to provide experimental estimates of (1) the pre-exponential frequency factor ƒ₀ in the Néel-Arhennius relaxation equation; (2) the SPM threshold size at room temperature for …

Single-Shot Detection Of Wavepacket Evolution, M. B. Campbell, Thomas J. Bensky, Robert R. Jones

Physics

We have developed a new instrument for monitoring electronic wavepacket dynamics using a single electromagnetic pulse pair. The operation of the device is analogous to that of single-shot cross-correlators commonly used to monitor the temporal evolution of short laser pulses. We have used the instrument to probe wavepacket evolution over time scales ranging from 100 psec to less than 1 fsec. The device reduces the amount of time required to collect pump-probe time delay data by orders of magnitude, greatly reducing the deleterious effects of experimental drifts. In addition, the single-shot feature provides real-time feedback as to the affect of …

Ionization Of Na Rydberg Atoms By Subpicosecond Quarter-Cycle Circularly Polarized Pulses, Thomas J. Bensky, G. Haeffler, Robert R. Jones

Physics

We report the first observation of ionization of Rydberg atoms by subpicosecond, circularly polarized THz radiation. The field amplitude in these pulses is non-negligible for only one-quarter of an optical cycle. The experiment is performed in the short-pulse regime, where the duration of the ionizing pulse is shorter than the classical Kepler period of the Rydberg electron. We find that the ionization probability for these atoms is remarkably insensitive to the time-varying polarization of the THz field.

Magneto-Aerotaxis In Marine Coccoid Bacteria, Richard B. Frankel, Dennis A. Bazylinski, Mark S. Johnson, Barry L. Taylor

Physics

Magnetotactic cocci swim persistently along local magnetic field lines in a preferred direction that corresponds to downward migration along geomagnetic field lines. Recently, high cell concentrations of magnetotactic cocci have been found in the water columns of chemically stratified, marine and brackish habitats, and not always in the sediments, as would be expected for persistent, downward-migrating bacteria. Here we report that cells of a pure culture of a marine magnetotactic coccus, designated strain MC-1, formed microaerophilic bands in capillary tubes and used aerotaxis to migrate to a preferred oxygen concentration in an oxygen gradient. Cells were able to swim in …

Review Of Possible Health Effects Of Exposure To Residential Electric And Magnetic Fields, David W. Hafemeister

Physics

No abstract provided.

Sea Brightness Temperature And Effects Of Spray And Whitecaps, Richard P. Barber Jr., Jin Wu

Physics

Following the approach of Tang [1974], the microwave brightness of the sea surface is recalculated with recent parameterizations in terms of wind velocity for the slope distribution and whitecap coverage of the sea surface and the contribution of sea spray. The difference between this revised calculation with no free parameters and the earlier one becomes more significant as the wind velocity increases; it reaches 10 K or more at a wind velocity of 20 m s-1. Present predictions compare favorably with experimental results, suggesting that this model does include the essential physical mechanisms.

Reflections On The Gao Report On The Nuclear Triad, David W. Hafemeister

Physics

Senate Hearings on the GAO report on the nuclear triad and on the START treaty showed that vulnerabilities of the U.S. triad were vastly over‐stated, that the performance of new projected strategic systems was over‐estimated, and that the performance of existing U.S. strategic systems was under‐estimated. These exaggerations enhanced the psychological (Freud) aspects of the Cold War and compromised logic (Newton).

With the end of the Cold War it is imperative that we re‐examine the basic premises that guided the choices of the strategic nuclear systems. The initial bottom line is that these systems were successful in that they did …

Review Of The Nuclear Black Market, Global Organized Crime Project, David W. Hafemeister

Physics

No abstract provided.

Summing Up: Questions And Answers On The Comprehensive Test Ban Treaty, David W. Hafemeister

Physics

My experiences with the ratification of the Strategic Arms Reduction Treaty, the Threshold Test Ban Treaty, and the Conventional Armed Forces in Europe Treaty have led me to conclude that presenting technical issues early in the process greatly reduces their politicization during the ratification end game. This chapter summarizes the important issues that will be raised during the debate on ratification of the Comprehensive Test Ban Treaty. It uses a compact question and answer format to cover the following topics: I. Nuclear Proliferation, II. Nuclear Arms Control, III. Warhead Reliability and Yield for National Security, IV. Warhead Safety, V. Verification, …

A Child's Flashlight And Rc Circuit Concepts, Matthew J. Moelter, Rand S. Worland

Physics

No abstract provided.

In Search Of An Improved Science And Public-Policy Process, David W. Hafemeister

Physics

No abstract provided.

The Current Energy Situation: Summary Points, David W. Hafemeister, A. Brecher, A. Fainberg, R. Howes, R. Socolow, D. Bodansky, P. Craig, B. Hammer, S. Smith, E. Stechel

Physics

Energy problems are now being largely ignored, despite their continuing importance. The near-disappearance of energy from the U.S. public agenda is apparent in the scant attention given to energy topics by the media and by public figures. Some suggestions for governmental action were stimulated by the rise in gasoline prices in the Spring of 1996, but the matter was treated as a short-term anomaly -- not as a harbinger of more severe difficulties to come. This lack of long term concern is perhaps natural, because fuel supplies are generally ample and prices are still relatively low, with the real cost …

Review Of Dark Sun: The Making Of The Hydrogen Bomb By Richard Rhodes, David W. Hafemeister

Physics

No abstract provided.

Magnetic Properties Of Tunicate Blood Cells. Ii. Ascidia Ceratodes, Kenneth Kustin, William E. Robinson, Richard B. Frankel, K. Spartalian

Physics

The magnetic properties of intact blood cells of the tunicate Ascidia ceratodes have been measured up to 50 kOe with a SQUID susceptometer. Analysis of total metal contents by plasma emission spectroscopy and V(IV) content by epr indicates that approximately 5% of the accumulated vanadium is +4 vanadyl ion. Measured values of the magnetic moment M_P at different values of the applied magnetic field H over the temperature range T = 2–100 K depend on the magnitude of the field indicating magnetic anisotropy of the ground state. The slope of the M_P vs. H/T curve at …

Resource Letter Belfef-1: Biological Effects Of Low-Frequency Electromagnetic Fields, David W. Hafemeister

Physics

This Resource Letter provides a guide to the literature on the interaction of extremely low-frequency electromagnetic field (ELF/EMF) interactions with biological matter, and on the possibility that such interactions could have a harmful effect on human health. Journal articles and books are cited for the following topics: ELF/EMF theoretical interactions with biological cells, organs and organisms, magnetic dipole interactions, sensing by animals, biomedical–biophysical experiments, epidemiology, and litigation–mitigation risk issues.

Charge Collection And Trapping In Low‐Temperature Silicon Detectors, M. J. Penn, Brian L. Dougherty, Blas Cabrera, R. M. Clarke, Betty A. Young

Physics

Charge collection efficiency measurements in silicon detectors at low temperature (T < 0.5 K) and low applied electric field (E=0.1–100 V/cm) were performed using a variety of high‐purity, p‐type silicon samples with room‐temperature resistivity in the range 2–40 kΩ cm. Good charge collection under these conditions of low temperature and low electric field is necessary for background suppression, through the simultaneous measurement of phonons and ionization, in a very low event rate dark matter search or neutrino physics experiment. Charge loss due to trapping during drift is present in some samples, but the data suggest that another charge–loss mechanism is also important. We present results which indicate that, for 60 keV energy depositions, a significant fraction of the total charge loss by trapping occurs in the initial electron‐hole cloud near the event location which may briefly act as a shielded, field‐free region. In addition, measurements of the lateral size, transverse to the applied electric field, of the initial electron‐hole cloud indicate large transverse diffusion lengths. At the lowest fields a lateral diameter on the order of 1 mm is found in a detector ∼5 mm thick.

Background Paper On "Power Line Fields And Public Health", David W. Hafemeister

Physics

No abstract provided.

Heat-Capacity And Magnetic Measurements On The Y(Ni2-XCoX)B2C System, C. C. Hoellwarth, P. Klavins, R. N. Shelton

Physics

We have performed field-and temperature-dependent magnetization, resistivity, and heat-capacity measurements on polycrystalline samples of the Y(Ni_2-xCo_x)B₂C system with 0.0≤x≤0.4. Values of T_c ,x₀,H_c2,Θ_D,λ and N(E_d) were determined for various samples. We observe that Θ_D increases with x, while all the other parameters decrease with x. The T_c vs x data can be described using the BCS theory and the measured values of N(E_f)and Θ_D. The results suggest that the decrease in T_c is due to the decrease in …

Biological Effects Of Static Magnetic Fields, Richard B. Frankel, Robert P, Liburdy

Physics

No abstract provided.

The Anomalous Mössbauer Fraction Of Ferritin And Polysaccharide Iron Complex (Pic), M. E. Y. Mohie-Eldin, Richard B. Frankel, L. Gunther, G. C. Papaefthymiou

Physics

Mössbauer studies of the ubiquitous protein molecule ferritin and its synthetic "biomimic" polysaccharide iron complex (PIC) exhibit an anomaly in the Mössbauer spectrum wherein the recoil free fraction f-factor has a sharp drop with respect to temperature as the temperature rises above 30 K for mammalian ferritin and 60 K for PIC. The anomaly coincides with the disappearance of hyperfine splitting, which is due to superparamagnetic relaxation above the blocking temperature. Different absorbers were used to experimentally investigate the effect of absorber thickness on the Mössbauer spectrum. The anomaly persists for thin absorbers. Also, spectra treated with FFT procedures …

A Quasiparticle Trap Assisted Transition Edge Sensor For Phonon Mediated Particle Detection, K. D. Irwin, S. W. Nam, Blas Cabrera, B. Chugg, Betty A. Young

Physics

ABSTRACT We have demonstrated the operation of composite superconducting tungsten and aluminum transition‐edge sensors which take advantage of quasiparticle trapping and electrothermal feedback. We call these devices W/Al QETs (quasiparticle‐trap‐assisted electrothermal feedback transition‐edge sensors). The quasiparticle trapping mechanism makes it possible to instrument large surface areas without increasing sensor heat capacity, thus allowing larger absorbers and reducing phonon collection times. The sensor consists of a 30‐nm‐thick superconducting tungsten thin film with T_c∼80 mK deposited on a high‐purity silicon substrate. The W film is patterned into 200 parallel lines segments, each 2 μm wide and 800 μm long. Eight …

Review Of Environmental Physics By Egbert Boeker And Rienk Van Grondelle, David W. Hafemeister

Physics

No abstract provided.

Remanence Measurements On Individual Magnetotactic Bacteria Using A Pulsed Magnetic Field, Ietje Penninga, Hendrik De Waard, Bruce M. Moskowitz, Dennis A. Bazylinski, Richard B. Frankel

Physics

We describe pulsed-magnetic-field remanence measurements of individual, killed, undisrupted cells of three different types of magnetotactic bacteria. The measurement technique involved the observation of aligned, individual magnetotactic bacteria with a light microscope as they were subjected to magnetic pulses of increasing amplitude. We show that for MM cells, the hysteresis loop is square, with the coercive field variable from cell to cell. This is consistent with just two magnetization states for the single chain of magnetite particles. For MR and MMP cells, the hysteresis loops are not square, indicating that there are several different magnetization states, and that individual cells …

Controlled Biomineralization Of Magnetite (Fe3O4) And Greigite (Fe3S4) In A Magnetotactic Bacterium, Dennis A. Bazylinski, Richard B. Frankel, Brigid R. Heywood, Stephen Mann, John W. King, Percy L. Donaghay, Alfred K. Hanson

Physics

A slowly moving, rod-shaped magnetotactic bacterium was found in relatively large numbers at and below the oxic-anoxic transition zone of a semianaerobic estuarine basin. Unlike all magnetotactic bacteria described to date, cells of this organism produce single-magnetic-domain particles of an iron oxide, magnetite (Fe₃O₄), and an iron sulfide, greigite (Fe₃O₄), within their magnetosomes. The crystals had different morphologies, being arrowhead or tooth shaped for the magnetite particles and roughly rectangular for the greigite particles, and were coorganized within the same chain(s) in the same cell with their long axes along the chain …