1,611 research outputs found
Current-carrying cosmic string loops 3D simulation: towards a reduction of the vorton excess problem
The dynamical evolution of superconducting cosmic string loops with specific
equations of state describing timelike and spacelike currents is studied
numerically. This analysis extends previous work in two directions: first it
shows results coming from a fully three dimensional simulation (as opposed to
the two dimensional case already studied), and it now includes fermionic as
well as bosonic currents. We confirm that in the case of bosonic currents,
shocks are formed in the magnetic regime and kinks in the electric regime. For
a loop endowed with a fermionic current with zero-mode carriers, we show that
only kinks form along the string worldsheet, therefore making these loops
slightly more stable against charge carrier radiation, the likely outcome of
either shocks or kinks. All these combined effects tend to reduce the number
density of stable loops and contribute to ease the vorton excess problem. As a
bonus, these effects also may provide new ways of producing high energy cosmic
rays.Comment: 11 pages, RevTeX 4 format, 8 figures, submitted to PR
Threats to groundwater supplies from contamination in Sierra Leone, with special reference to Ebola care facilities
The outbreak of Ebola virus disease in West Africa in 2014 is the worst single outbreak recorded, and has resulted in more fatalities than all previous outbreaks combined. This outbreak has resulted in a large humanitarian effort to build new health care facilities, with associated water supplies. Although Ebola is not a water-borne disease, care facilities for Ebola patients may become sources of outbreaks of other, water-borne, diseases spread through shallow groundwater from hazard sources such as open defecation, latrines, waste dumps and burial sites to water supplies.
The focus of this rapid desk study is to assess from existing literature the evidence for sub-surface transport of pathogens in the context of the hydrogeological and socio-economic environment of Sierra Leone. In particular, the outputs are to advise on the robustness of the evidence for an effective single minimum distance for lateral spacing between hazard sources and water supply, and provide recommendations for protecting water supplies for care facilities as well as other private and public water supplies in this region. Preliminary conclusions were:
Considering the climate (heavy intense rainfall for 8 months), the hydrogeological conditions (prevalent shallow and rapidly fluctuating water tables, permeable tropical soils), the pervasive and widespread sources of hazards (very low improved sanitation coverage), and the widespread use of highly vulnerable water points there is little evidence that simply using an arbitrary lateral spacing between hazard sources and water point of 30 – 50 m would provide effective protection for groundwater points.
An alternative framework that considers vertical as well as lateral separation and the integrity of the construction and casing of the deeper water points is recommended to protect water supplies from contamination by pathogens.
The shallow aquifer, accessed by wells and springs, must be treated as highly vulnerable to pollution, both from diffuse sources and from localised sources.
Diffuse pollution of groundwater from surface-deposited wastes including human excreta is likely to be at least as important as pollution from pit latrines and other point sources, given the low sanitation coverage in Sierra Leone.
Even though conditions are not optimal for pathogen survival (e.g. temperatures of >25° C), given the very highly permeable shallow tropical soil zone, and the high potential surface and subsurface loading of pathogens, it is likely that shallow water sources are at risk from pathogen pollution, particularly during periods of intense rainfall and high water table conditions.
Extending improved sanitation must be a high priority, in conjunction with improved vertical separation between hazard sources and water points, in order to reduce environmental contamination and provide a basis for improved public health.
We recommend that risk assessments of water points are undertaken for health care facilities as soon as possible including: detailed sanitary inspections of water points within the 30 – 50 m radius suggested by the Ministry of Water Resource; assessments of the construction and integrity of the water points; a wider survey of contaminant load and rapid surface / sub surface transit routes within a wider 200 m radius of water points.
Analysis of key water quality parameters and monitoring of water levels should be undertaken at each water point in parallel with the risk assessments.
The translation of policy on water, sanitation and hygiene into implementation needs complementary research to understand key hydrogeological processes as well as barriers and failings of current practice for reducing contamination in water points. A baseline assessment of water quality status and sanitary risks for e.g. wells vs boreholes, improved vs unimproved sources in Sierra Leone is needed. Understanding the role of the tropical soil zone in the rapid migration of pollutants in the shallow subsurface, i.e. tracing rapid pathways, and quantifying residence times of shallow and deep groundwater systems are key knowledge gaps
The incidence of wind erosion as related to soil properties and geomorphic history in south-western Australia
Effect of Time and Amount of Nitrogen Uptake on Sugarbeet Growth and Yield
Sugarbeet (Beta vulgaris L.) root quality has been
steadily decreasing since the early 1951's with increased
use of N fertilizer. Since the extent of these decreases
may be associated with the time and amount of N uptake,
the objective of this study was to evaluate the
effects of several rates and times of N fertilizer applications
and N uptake by sugarbeets on seasonal growth
rates, sucrose percentage and accumulation, dry matter
production, and partitioning of the photosynthate.
Sugarbeets were grown under field conditions on a
Portneuf silt loam soil (Durixerollic Calciorthids, coarse-silty,
mixed, mesic) near Twin Falls, Idaho, in 1977,
using four N rates, each applied preplant, mid-June,
mid-July, and mid-August. Root yields, sucrose concentration
and yield, dry matter production, leaf area index,
and plant N uptake were determined from samples
taken throughout the season. Adding N fertilizer above
that needed for optimum plant growth or delaying N
application until midseason caused a greater proportion
of the photosynthate to be used for increased top growth
at the expense of dry matter and sucrose accumulation
in the roots. Sucrose accumulation was maximum from
late July until early September; therefore, during this
period, addition of N and N uptake by the plant caused
the greatest decrease in sucrose accumulation and production
at harvest. Increasing N levels decreased sucrose concentrations
during the season and at harvest because of
1) increased moisture level of roots, and 2) dry matter
produced and accumulated in the roots having a decreased
sucrose concentration. The rate of accumulation
of stored sucrose was reduced by midseason N application,
but stored sucrose was not used for increased
growth of beet tops. Excess and late N applications also
increased impurities in the beet root, decreasing extractability
of stored sucrose, which further decreased refined
sucrose production. Early application of N fertilizer at
optimum levels should maximize refined sucrose production
Yield and Quality as Affected by Early and Late Fall and Spring Harvest of Sugarbeets
Sugarbeets (Beta vulgaris L.) in the intermountain
areas of the western United States are normally planted in
early spring and harvested during October with the advent
of cool temperatures. The beet roots during this harvesting
period are near their maximum yield and sucrose concentration.
Temperatures are cool and suitable for
storing excess roots in piles for later processing. The
factory processing of beet roots is presently limited to
the period between harvest and mid-February after which
stored roots in piles deteriorate rapidly in quality with
increased temperatures (2, 10, 16, 17).
The closing of some sugar factories, and low prices
currently received for other crops, has intensified demand
by farm managers for increased acreage allotment for
sugarbeets. Present low world sugar prices and the uncertainty
of continued sugar legislation discourages the expansion
of the cutting and processing facilities in factories.
Methods and procedures are needed to increase the
tonnage of beet roots that can be processed using existing
equipment and facilities.
The objective of this study was to evaluate methods
and procedures where factories can increase the amount of
beet roots processed with existing equipment by methods
such as early and late fall and spring harvest of
sugarbeets
Sugarbeet Yield and Seasonal Growth Characteristics as Affected by Hail Damage and Nitrogen Level
Sugarbeets (Beta vulgaris L.) grown in the western United
States are subject to hailstorms that reduce yield and profits to the
grower. A better understanding of growth characteristics before
and after hail damage will enable growers to make correct decisions
regarding soil and plant treatments to hasten recovery from hail
damage and maximize sucrose yields
Effect of Mid-to Late-Season Water Stress on Sugarbeet Growth and Yield
Costs of irrigation (labor, water, and energy) and sometimes
limited-late-season water are factors associated with
the choice of crop and economic returns. Sugarbeets
(Beta vulgaris L.) have shown certain tolerance to water
stress, therefore the objective of this study was to evaluate
growth rates and characteristics, sucrose accumulation,
and N uptake by sugarbeets grown under mid to
late-season soil water deficit and plant water stress.
Sugarbeets were grown in a field experiment on a
Portneuf silt loam soil (Durixerollic Calciorthids; coarse-silty,
mixed, mesic) under normal irrigation until 15
July, after which further irrigation was terminated or
reduced on two treatments during a 2-year period. Root
yield, sucrose concentration, sucrose yield, plant N uptake,
and petiole NO?-N were determined from samples
taken throughout each season. These experiments demonstrated
that very little, if any, sucrose yield reduction
can be expected in the Idaho area if irrigations are discontinued
after filling the soil profile with water about
1 August and if the soil contains at least 200 mm of
available water to a soil depth of 160 cm. During dry
years, there may be an advantage to applying a light
irrigation about 1 month after water cutoff and to have
sufficient surface soil water present at harvest to prevent
loss of roots by breaking. Use of deficit water management
during August, September, and October curtailed
leaf growth, reduced leaf area when no longer needed,
reduced N uptake from the soil, increased sucrose concentration
in the beet root, and decreased fresh root
yield. These effects on yields were mainly caused by dehydration
of the beet tops and roots so sucrose production
was scarcely affected even though only 74% of the normal
irrigation water was applied. Limited irrigations reduced
evapotranspiration rates because of drier surface soil and
partial stomatal closure, thereby decreasing the rate of
water extraction from the soil reservoir by the plant. Use
of mid to late-season deficit water management could
substantially reduce sugarbeet production costs in irrigated
areas and economically benefit the consumer, producer,
and manufacturer
Root and Sucrose Yields of Sugarbeets as Affected by Mid-to-Late-Season Water Stress
Investigations of the irrigation water requirement of sugarbeets
(Beta vulgaris L.) in Arizona and California have shown
that water stress several weeks before harvest of fall-planted beets
reduces root yields but increases sucrose concentration (2,3).
Their studies showed that, since soil and plant water stress late
in the season did not significantly reduce sucrose production,
irrigations could be discontinued 3 to 4 weeks before harvest for
maximum water economy. Mid- to late-season water deficit studies
on spring-planted sugarbeets at this Center in 1977 and 1978
clearly showed that sucrose yield was reduced very little in this
area, if at all, if irrigations were discontinued after the soil
profile was filled with water about 1 August or 10 to 12 weeks
before harvest, on soil having a useable soil water reservoir of
at least 200 mm (1) . However, if no rainfall occurs, a light
irrigation about 1 month after water cutoff may be advantageous.
The major difference between these two areas (Arizona-California
and Idaho) is that in Arizona and California, potential evapotranspiration
rates are higher and increasing when fall-planted
beets are harvested; whereas in Idaho, potential rates are lower
and decreasing when spring-planted beets are harvested. Allowing
mid- to late-season water stress to develop in the Idaho area
reduces irrigation water requirements by about 30% during August,
September, and October when irrigation water and hydro-electric
power for pumping are in shortest supply. Other recent investigations
also show the drought tolerance of sugarbeets throughout
the growing season ( 8, 11)
Cometary charge exchange diagnostics in UV and X‐ray
Since the initial discovery of cometary charge exchange emission, more than 20 comets have been observed with a variety of X‐ray and UV observatories. This observational sample offers a broad variety of comets, solar wind environments and observational conditions. It clearly demonstrates that solar wind charge exchange emission provides a wealth of diagnostics, which are visible as spatial, temporal, and spectral emission features. We review the possibilities and limitations of each of those in this contribution (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/91138/1/335_ftp.pd
Edge states of graphene bilayer strip
The electronic structure of the zig-zag bilayer strip is analyzed. The
electronic spectra of the bilayer strip is computed. The dependence of the edge
state band flatness on the bilayer width is found. The density of states at the
Fermi level is analytically computed. It is shown that it has the singularity
which depends on the width of the bilayer strip. There is also asymmetry in the
density of states below and above the Fermi energy.Comment: 9 page
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