62,865 research outputs found
Sonic Layer Depth estimated from XBT temperatures and climatological salinities
Sonic layer depth (SLD) plays an important role in antisubmarine warfare in terms of identifying the shadow zones for submarine safe parking. SLD is estimated from sound velocity profiles (SVP) which is in turn obtained from temperature and salinity (T/S) profiles. Given the limited availability of salinity data in comparison to temperature, SVPs need to be obtained from alternate methods. In the present work, to make use of voluminous temperature data sets from XBT, CTD and other source for estimating SLD, we propose a method of utilizing XBT measurements and World Ocean Atlas climatological salinities to compute SVP and then extract SLD. This approach is demonstrated by utilizing T/S data from Argo floats in the Arabian Sea (40° – 80° E and 0 – 30° N). SLD is estimated from SVP obtained from Argo T/S profiles first and again by replacing the Argo salinity with climatological salinity. It is found that in more than 90% of cases, SLD matched exactly, with the root mean square deviation ranging from 3 – 12 m with an average of 7 m
TVS-cone metric spaces as a special case of metric spaces
There have been a number of generalizations of fixed point results to the so
called TVS-cone metric spaces, based on a distance function that takes values
in some cone with nonempty interior (solid cone) in some topological vector
space. In this paper we prove that the TVS-cone metric space can be equipped
with a family of mutually equivalent (usual) metrics such that the convergence
(resp. property of being Cauchy sequence, contractivity condition) in TVS sense
is equivalent to convergence (resp. property of being Cauchy sequence,
contractivity condition) in all of these metrics. As a consequence, we prove
that if a topological vector space and a solid cone are given, then the
category of TVS-cone metric spaces is a proper subcategory of metric spaces
with a family of mutually equivalent metrics (Corollary 3.9). Hence,
generalization of a result from metric spaces to TVS-cone metric spaces is
meaningless. This, also, leads to a formal deriving of fixed point results from
metric spaces to TVS-cone metric spaces and makes some earlier results vague.
We also give a new common fixed point result in (usual) metric spaces context,
and show that it can be reformulated to TVS-cone metric spaces context very
easy, despite of the fact that formal (syntactic) generalization is impossible.
Apart of main results, we prove that the existence of a solid cone ensures that
the initial topology is Hausdorff, as well as it admits a plenty of convex open
sets. In fact such topology is stronger then some norm topology.Comment: 14 page
Opportunities and limitations of transition voltage spectroscopy: a theoretical analysis
In molecular charge transport, transition voltage spectroscopy (TVS) holds
the promise that molecular energy levels can be explored at bias voltages lower
than required for resonant tunneling. We investigate the theoretical basis of
this novel tool, using a generic model. In particular, we study the length
dependence of the conducting frontier orbital and of the 'transition voltage'
as a function of length. We show that this dependence is influenced by the
amount of screening of the electrons in the molecule, which determines the
voltage drop to be located at the contacts or across the entire molecule. We
observe that the transition voltage depends significantly on the length, but
that the ratio between the transition voltage and the conducting frontier
orbital is approximately constant only in strongly screening (conjugated)
molecules. Uncertainty about the screening within a molecule thus limits the
predictive power of TVS. We furthermore argue that the relative length
independence of the transition voltage for non-conjugated chains is due to
strong localization of the frontier orbitals on the end groups ensuring binding
of the rods to the metallic contacts. Finally, we investigate the
characteristics of TVS in asymmetric molecular junctions. If a single level
dominates the transport properties, TVS can provide a good estimate for both
the level position and the degree of junction asymmetry. If more levels are
involved the applicability of TVS becomes limited.Comment: 8 pages, 12 figure
Improving Transition Voltage Spectroscopy of Molecular Junctions
Transition voltage spectroscopy (TVS) is a promising spectroscopic tool for
molecular junctions. The principles in TVS is to find the minimum on a
Fowler-Nordheim plot where is plotted against and relate the
voltage at the minimum, , to the closest molecular level.
Importantly, , is approximately half the voltage required to see a
peak in the curve. Information about the molecular level position can
thus be obtained at relatively low voltages. In this work we show that the
molecular level position can be determined at even lower voltages, by finding the minimum of with .
On the basis of a simple Lorentzian transmission model we analyze theoretical
{\it ab initio} as well as experimental curves and show that the voltage
required to determine the molecular levels can be reduced by as
compared to conventional TVS. As for conventional TVS, the symmetry/asymmetry
of the molecular junction needs to be taken into account in order to gain
quantitative information. We show that the degree of asymmetry may be estimated
from a plot of vs. .Comment: 6 pages, 8 figure
Specialist tissue viability services: a priority or a luxury?
During the 1980s, the number of tissue viability nurses (TVNs) rose steadily in the UK, in response to mismanagement of patients with wounds (Fletcher, 1995). Since this time, and in response to the quality agenda, the necessity of promoting a tissue viability service (TVS) that is able to meet the needs of a changing population, while being cost effective and offering interventions based on research and evidence, has grown. The drive to reduce avoidable harm in healthcare and to make efficiency savings is continuing, with TVS being one of the key areas to deliver these targets. However, across the UK we have a wide range of role descriptions and job titles, yet little clarification as to the qualifications and skills required to deliver a successful TVS. Infection control specialist nurses have a clear identity with concise role descriptions representing a range of pay bands. Arguably, this is because they are aligned with a medical specialty, whereas TV is not. The introduction of âAny Qualified Providerâ (Department of Health, 2011) has witnessed some services, including management of leg ulceration, being delivered by non-NHS providers at a reduced cost. So is TVS in danger of becoming more of a ânice thingâ rather than a priority
Quantifying Transition Voltage Spectroscopy of Molecular Junctions
Transition voltage spectroscopy (TVS) has recently been introduced as a
spectroscopic tool for molecular junctions where it offers the possibility to
probe molecular level energies at relatively low bias voltages. In this work we
perform extensive ab-initio calculations of the non-linear current voltage
relations for a broad class of single-molecule transport junctions in order to
assess the applicability and limitations of TVS. We find, that in order to
fully utilize TVS as a quantitative spectroscopic tool, it is important to
consider asymmetries in the coupling of the molecule to the two electrodes.
When this is taken properly into account, the relation between the transition
voltage and the energy of the molecular orbital closest to the Fermi level
closely follows the trend expected from a simple, analytical model.Comment: 5 pages, 4 figures. To appear in PR
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