15,366 research outputs found
Circuit prevents overcharging of secondary cell batteries
Circuit prevents battery cell overcharging by detecting and reducing the charging voltage to the open-circuit voltage of the battery when this current falls to a predetermined value. The voltage control depends on the fact that the charging current falls significantly when the battery nears its fully charged state
Method and apparatus for battery charge control Patent
Battery charging system with cell to cell voltage balanc
Shock induced formation of MgAl_2O_4 spinel from oxides
The physics of mineral grain sliding, which occurs upon dynamic compression of rocks, is investigated by shock loading single crystals of corundum (Al_2O_3) and periclase (MgO) in contact obliquely in impact experiments. Energy dispersive X-ray analysis and X-ray diffraction studies of samples recovered from 26â36 GPa, 800 ns experiments indicated that under certain conditions a spinel phase of composition MgAl_2O_4 and thickness â€20 ”m was produced at the interface between the two crystals. Although the computed shock (continuum) temperatures were below those necessary to melt the initial oxides, the spinel nonetheless appears to have formed as a result of localised melting, via grain boundary sliding friction, followed by rapid quenching. Scanning electron microscopy (SEM) revealed some evidence for such melting. Moreover, the timescale of the experiments is too short for solid state diffusion (during the shock state) to explain the observed spinel thickness, although defect enhanced solid state diffusion, subsequent to loading and unloading, remains a possibility. The results also reinforce other recent observations and theories of heterogeneous deformation in minerals
The effect of two-temperature post-shock accretion flow on the linear polarization pulse in magnetic cataclysmic variables
The temperatures of electrons and ions in the post-shock accretion region of
a magnetic cataclysmic variable (mCV) will be equal at sufficiently high mass
flow rates or for sufficiently weak magnetic fields. At lower mass flow rates
or in stronger magnetic fields, efficient cyclotron cooling will cool the
electrons faster than the electrons can cool the ions and a two-temperature
flow will result. Here we investigate the differences in polarized radiation
expected from mCV post-shock accretion columns modeled with one- and
two-temperature hydrodynamics. In an mCV model with one accretion region, a
magnetic field >~30 MG and a specific mass flow rate of ~0.5 g/cm/cm/s, along
with a relatively generic geometric orientation of the system, we find that in
the ultraviolet either a single linear polarization pulse per binary orbit or
two pulses per binary orbit can be expected, depending on the accretion column
hydrodynamic structure (one- or two-temperature) modeled. Under conditions
where the physical flow is two-temperature, one pulse per orbit is predicted
from a single accretion region where a one-temperature model predicts two
pulses. The intensity light curves show similar pulse behavior but there is
very little difference between the circular polarization predictions of one-
and two-temperature models. Such discrepancies indicate that it is important to
model some aspect of two-temperature flow in indirect imaging procedures, like
Stokes imaging, especially at the edges of extended accretion regions, were the
specific mass flow is low, and especially for ultraviolet data.Comment: Accepted for publication in Astrophysics & Space Scienc
Moderate velocity oblique impact sliding: Production of shocked meteorite textures and palaeomagnetically important metallic spherules in planetary regoliths
We detail the production of metallic spherules in laboratory oblique shock impact experiments, and their applicability (1) to textures in a partly shock-melted chondritic meteorite and (2) to the occurrence of palaeomagnetically important fine iron or iron alloy particles in the lunar regolith. Samples recovered from 29â44 GPa, 800 ns, experiments revealed melting and textures reminiscent of metallic spherules in the Yanzhuang H-chondrite, including âdumbbellâ forms and other more complex morphologies. Our experiments demonstrate that metallic spherules can be produced via oblique impact sliding at lower velocities (1.85 km s^(â1)) than are generally assumed in previous work associated with bulk-shock melting, and that oblique impact sliding is a viable mechanism for producing spherules in shock-induced veins in moderately shocked meteorites. Significantly, our experiments also produced fine metallic (iron alloy) spherules within the theoretical narrow size range (a few tens of nanometers for slightly ellipsoidal particles) for stable single-domain (SSD) particles, which are the most important palaeomagnetically, since they can record lunar and planetary magnetic fields over geological time periods. The experiments also produced spherules consistent with superparamagnetic (SP) and multidomain (MD) particle sizes. The fine SSD and SP particles on the lunar surface are currently thought to have been formed predominantly by space weathering processes. Our experiments suggest that oblique shock impact sliding may be a further means of producing the SSD and SP iron or iron alloy particles observed in the lunar regolith, and which are likely to occur in the regoliths of Mercury and other planetary bodies
Shock consolidation of diamond and graphite mixtures to fused polycrystalline diamond
The production of fused compacts of polycrystalline diamond was achieved by subjecting porous (35%â49% porosity) mixtures of diamond crystals plus graphite (13â16 wt. %) to dynamic shock pressures of 10â18 GPa. The recovered material from an initial mixture of 4â8-”m diamond crystals plus graphite revealed a very homogeneous texture with little evidence of original grain boundaries. The preconsolidation addition of graphite also allowed ultrafine (<5 ”m) diamond crystals to be consolidated; this was not previously possible with the use of diamond crystals alone. The results are consistent with calculations which suggest that a thin layer of graphite surrounding a diamond crystal delays thermal equilibrium between the surface and interior of the diamond crystal, thus allowing greater surface heating. Consolidation is also probably enhanced by conversion of graphite to diamond, possibly via the liquid state
Imaging Polarimetric Observations of a New Circumstellar Disk System
Few circumstellar disks have been directly observed. Here we use sensitive
differential polarimetric techniques to overcome atmospheric speckle noise in
order to image the circumstellar material around HD 169142. The detected
envelope or disk is considerably smaller than expectations based on the
measured strength of the far-IR excess from this system
Prevalence of and risk factors for acute laminitis in horses treated with corticosteroids
A retrospective treated versus untreated study (study 1) and multicentre prospective cohort study (study 2) were undertaken to determine the prevalence of, and risk factors associated with, acute laminitis in horses treated with corticosteroids. All old treated with corticosteroids JanuaryâDecember 2014 (study 1) and January 2015âFebruary 2017 (study 2) by two first opinion and referral hospitals in UK were included. Additionally, an untreated animal was identified for each treated animal (study one). Signalment, body condition (study 2 only), relevant medical history, primary condition, corticosteroid therapy prescribed and occurrence of acute laminitis during or within 14 days of cessation of corticosteroid treatment were recorded.
For study 1, 205 cases and 205 controls were identified; two animals within each group (1 per cent) developed laminitis. In total, 1565 animals were included in study 2; laminitis period prevalence was 0.6 per cent (95 per cent CI 0.4 per cent to 1.2 per cent), with 10 cases in 1565 treated animals. There were significant associations between laminitis and breed (pony vs horse; p=0.01; univariable analysis only), the presence of a laminitis risk factor (history of laminitis or an underlying endocrinopathy; p<0.001; OR (95 per centâCI) 18.23 (5.05 to 65.87)) and body condition (overweight/obese vs not; p=0.04; OR (95 per centâCI) 4.0 (1.09 to 14.75))
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Change in Distance to Nearest Facility and Abortion in Texas, 2012 to 2014
This Research Letter demonstrates that increases in travel distance to the nearest abortion clinic caused by clinic closures between 2012 and 2014 were closely associated with decreases in the official number of abortions in Texas. Counties where the distance to the nearest facility increased 100 miles or more between 2012 and 2014 saw a 50% decline in abortions. Meanwhile, counties that did not have an abortion provider in 2014 and did not experience a change in distance to the nearest facility had essentially no change in the number of abortions.Population Research Cente
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