1,416 research outputs found
Collective pinning of imperfect vortex lattices by material line defects in extreme type-II superconductors
The critical current density shown by a superconductor at the extreme type-II
limit is predicted to follow an inverse square-root power law with external
magnetic field if the vortex lattice is weakly pinned by material line defects.
It acquires an additional inverse dependence with thickness along the line
direction once pinning of the interstitial vortex lines by material point
defects is included. Moderate quantitative agreement with the critical current
density shown by second-generation wires of high-temperature superconductors in
kG magnetic fields is achieved at liquid-nitrogen temperature.Comment: 10 pages, 3 figures, 2 tables. To appear in Physical Review
Contamination of spacecraft by recontact of dumped liquids
Liquids partially freeze when dumped from spacecraft producing particles which are released into free space at various velocities. Recontact of these particles with the spacecraft is possible for specific particle sizes and velocities and, therefore, can become contamination for experiments within the spacecraft or released experiments as a result of waste and potable water dumped from Space Shuttle. An examination of dump characteristics was conducted on STS-29 using both on-board video records and ground based measurements. A preliminary analysis of data from this flight indicates particle velocities are in the range of 30 to 75 ft/sec and recontact is possible for limited particle sizes
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Employee performance management: charting the field from 1998 to 2018
Purpose: The purpose of this paper is to study the development and consider the future of one of the most controversial areas of human resource development – employee performance management (PM).
Design/methodology/approach: Through bibliometrics, a multiple correspondence analysis identifies the main research directions of PM studies and provides a map of descriptors and a list of authors, along with a framework to track PM literature over 20 years (1998–2018).
Findings: Scholars have attempted to address some of the questions raised by earlier researchers. However, critical questions remain unanswered, and there is increasing dissatisfaction with the process. The most glaring yet unaddressed problem with PM is poor employee acceptability of the process.
Practical implications: If the research gaps are addressed, the lack of acceptability of the PM could be resolved and more effectively managed in the future.
Originality/value: The study particularly addresses poor employee “acceptability” of the PM process, a subject that has received limited attention by scholars
Options for Improved Biomass Production in Feeding Systems for Dairying in High Rainfall Environments in New Zealand
New Zealand dairy production has expanded into marginal climates and soil types on the premise of excellent profitability and efficient utilisation of forage. Annual pasture production in the cool West Coast of the South Island (rainfall 2042-2933 mm) is15,000 kg. Increased farm production and feeding of high quality biomass, from imported feed or supplementary feed crops grown on- farm, are needed to improve milk solid output. Small plot trials with spring and early summer-sown brassicas, cereals and maize were the focus for development of systems to maximise and manage the seasonal feed supply. The effect of sowing time, fertiliser timing and rate of N and K fertiliser application were studied to quantify the risks of crop failure in the high rainfall and low radiation environment. The aim was to increase forage supply/ha in a predominantly grass-based system and reduce associated risks to environmental sustainability
Reflectivity and Microwave Absorption in Crystals with Alternating Intrinsic Josephson Junctions
We compute the frequency and magnetic field dependencies of the reflectivity
in layered superconductors with two alternating intrinsic Josephson
junctions with different critical current densities and quasiparticle
conductivities for the electric field polarized along the c-axis. The parameter
describing the electronic compressibility of the layers and the charge
coupling of neighboring junctions was extracted for the
SmLaSrCuO superconductor from two independent
optical measurements, the fit of the loss function at zero magnetic
field and the magnetic field dependence of the peak positions in .
The experiments are consistent with a free electron value for near
the Josephson plasma frequencies.Comment: 4 pages, 4 postscript figures, misprints in table correcte
Robotic-assistance does not enhance standard laparoscopic technique for right-sided donor nephrectomy.
OBJECTIVE: To examine donor and recipient outcomes after right-sided robotic-assisted laparoscopic donor nephrectomy (RALDN) compared with standard laparoscopic donor nephrectomy (LDN) and to determine whether robotic-assistance enhances LDN.
MATERIALS & METHODS: From December 2005 to January 2011, 25 patients underwent right-sided LDN or RALDN. An IRB-approved retrospective review was performed of both donor and recipient medical charts. Primary endpoints included both intraoperative and postoperative outcomes.
RESULTS: Twenty right-sided LDNs and 5 RALDNs were performed during the study period. Neither estimated blood loss (76.4 mL vs. 30 mL, P = .07) nor operative time (231 min vs. 218 min, P = .61) were significantly different between either group (LDN vs. RALDN). Warm ischemia time for LDN was 2.6 min vs. 3.8 min for RALDN (P = .44). Donor postoperative serum estimated glomerular filtration rates (eGFR) were similar (53 vs. 59.6 mL/min/1.73 m2, LDN vs. RALDN, P = .26). For the recipient patients, posttransplant eGFR were similar at 6 months (53.4 vs. 59.8 mL/min/1.73 m2, LDN vs. RALDN, P = .53).
CONCLUSION: In this study, robotic-assistance did not improve outcomes associated with LDN. Larger prospective studies are needed to confirm any perceived benefit of RALDN
Optical Properties of Crystals with Spatial Dispersion: Josephson Plasma Resonance in Layered Superconductors
We derive the transmission coefficient, , for grazing incidence of
crystals with spatial dispersion accounting for the excitation of multiple
modes with different wave vectors for a given frequency . The
generalization of the Fresnel formulas contains the refraction indices of these
modes as determined by the dielectric function . Near
frequencies , where the group velocity vanishes, depends
also on an additional parameter determined by the crystal microstructure. The
transmission is significantly suppressed, if one of the excited modes is
decaying into the crystal. We derive these features microscopically for the
Josephson plasma resonance in layered superconductors.Comment: 4 pages, 2 figures, epl.cls style file, minor change
Western equatorial African forest-savanna mosaics: a legacy of late Holocene climatic change?
Past vegetation and climate changes reconstructed using two pollen records from Lakes Maridor and Nguène, located in the coastal savannas and inland rainforest of Gabon, respectively, provide new insights into the environmental history of western equatorial African rainforests during the last 4500 cal yr BP. These pollen records indicate that the coastal savannas of western equatorial Africa did not exist during the mid-Holocene and instead the region was covered by evergreen rainforests. From ca. 4000 cal yr BP a progressive decline of inland evergreen rainforest, accompanied by the expansion of semi-deciduous rainforest, occurred synchronously with grassland colonisation in the coastal region of Gabon. The contraction of moist evergreen rainforest and the establishment of coastal savannas in Gabon suggest decreasing humidity from ca. 4000 cal yr BP. The marked reduction in evergreen rainforest and subsequent savanna expansion was followed from 2700 cal yr BP by the colonization of secondary forests dominated by the palm, <i>Elaeis guineensis</i>, and the shrub, <i>Alchornea cordifolia</i> (Euphorbiaceae). A return to wetter climatic conditions from about 1400 cal yr BP led to the renewed spread of evergreen rainforest inland, whereas a forest-savanna mosaic still persists in the coastal region. There is no evidence to suggest that the major environmental changes observed were driven by human impact
Accumulation of driver and passenger mutations during tumor progression
Major efforts to sequence cancer genomes are now occurring throughout the
world. Though the emerging data from these studies are illuminating, their
reconciliation with epidemiologic and clinical observations poses a major
challenge. In the current study, we provide a novel mathematical model that
begins to address this challenge. We model tumors as a discrete time branching
process that starts with a single driver mutation and proceeds as each new
driver mutation leads to a slightly increased rate of clonal expansion. Using
the model, we observe tremendous variation in the rate of tumor development -
providing an understanding of the heterogeneity in tumor sizes and development
times that have been observed by epidemiologists and clinicians. Furthermore,
the model provides a simple formula for the number of driver mutations as a
function of the total number of mutations in the tumor. Finally, when applied
to recent experimental data, the model allows us to calculate, for the first
time, the actual selective advantage provided by typical somatic mutations in
human tumors in situ. This selective advantage is surprisingly small, 0.005 +-
0.0005, and has major implications for experimental cancer research
The sensitivity of estuarine aragonite saturation state and pH to the carbonate chemistry of a freshet-dominated river
Ocean acidification threatens to reduce pH and aragonite saturation state
(ΩA) in estuaries, potentially damaging their ecosystems.
However, the impact of highly variable river total alkalinity (TA) and
dissolved inorganic carbon (DIC) on pH and ΩA in these
estuaries is unknown. We assess the sensitivity of estuarine surface pH and
ΩA to river TA and DIC using a coupled biogeochemical model
of the Strait of Georgia on the Canadian Pacific coast and place the results
in the context of global rivers. The productive Strait of Georgia estuary has
a large, seasonally variable freshwater input from the glacially fed,
undammed Fraser River. Analyzing TA observations from this river plume and pH
from the river mouth, we find that the Fraser is moderately alkaline
(TA 500–1000 µmol kg−1) but relatively DIC-rich. Model
results show that estuarine pH and ΩA are sensitive to
freshwater DIC and TA, but do not vary in synchrony except at high
DIC : TA. The asynchrony occurs because increased freshwater TA is
associated with increased DIC, which contributes to an increased estuarine
DIC : TA and reduces pH, while the resulting higher carbonate ion
concentration causes an increase in estuarine ΩA. When
freshwater DIC : TA increases (beyond ∼ 1.1), the shifting chemistry
causes a paucity of the carbonate ion that overwhelms the simple
dilution/enhancement effect. At this high DIC : TA ratio, estuarine
sensitivity to river chemistry increases overall. Furthermore, this increased
sensitivity extends to reduced flow regimes that are expected in future.
Modulating these negative impacts is the seasonal productivity in the estuary
which draws down DIC and reduces the sensitivity of estuarine pH to
increasing DIC during the summer season
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