2,615 research outputs found
Hydrogen atom in phase space. The Kirkwood-Rihaczek representation
We present a phase-space representation of the hydrogen atom using the
Kirkwood-Rikaczek distribution function. This distribution allows us to obtain
analytical results, which is quite unique because an exact analytical form of
the Wigner functions corresponding to the atom states is not known. We show how
the Kirkwood-Rihaczek distribution reflects properties of the hydrogen atom
wave functions in position and momentum representations.Comment: 5 pages (and 5 figures
Case study of the development of polar stratospheric clouds using bistatic imaging
International audienceThe formation of polar stratospheric clouds (PSCs) is closely related to wave activity on different scales since waves propagating into the stratosphere perturb the temperature profile. We present here a case study of the development of visible PSCs (mother-of-pearl clouds), appearing at the polar vortex edge on 9 January 1997, under-taken by means of ground-based cameras. It is shown that the presence of stratospheric clouds may be detected semi-automatically and that short-term dynamics such as altitude variations can be tracked in three dimensions. The PSC field showed distinct features separated by approximately 20 km, which implies wave-induced temperature variations on that scale. The wave-induced characteristics were further emphasised by the fact that the PSCs moved within a sloping spatial surface. The appearance of visible mother-of-pearl clouds seems to be related to leewave-induced cooling of air masses, where the synoptic temperature has been close to (but not necessarily below) the threshold temperatures for PSC condensation
The intermittent behavior and hierarchical clustering of the cosmic mass field
The hierarchical clustering model of the cosmic mass field is examined in the
context of intermittency. We show that the mass field satisfying the
correlation hierarchy is intermittent if , where is the dimension of the field, and is the power-law
index of the non-linear power spectrum in the discrete wavelet transform (DWT)
representation. We also find that a field with singular clustering can be
described by hierarchical clustering models with scale-dependent coefficients
and that this scale-dependence is completely determined by the
intermittent exponent and . Moreover, the singular exponents of a field
can be calculated by the asymptotic behavior of when is large.
Applying this result to the transmitted flux of HS1700 Ly forests, we
find that the underlying mass field of the Ly forests is significantly
intermittent. On physical scales less than about 2.0 h Mpc, the observed
intermittent behavior is qualitatively different from the prediction of the
hierarchical clustering with constant . The observations, however, do show
the existence of an asymptotic value for the singular exponents. Therefore, the
mass field can be described by the hierarchical clustering model with
scale-dependent . The singular exponent indicates that the cosmic mass
field at redshift is weakly singular at least on physical scales as
small as 10 h kpc.Comment: AAS Latex file, 33 pages,5 figures included, accepted for publication
in Ap
Targeted free energy perturbation
A generalization of the free energy perturbation identity is derived, and a
computational strategy based on this result is presented. A simple example
illustrates the efficiency gains that can be achieved with this method.Comment: 8 pages + 1 color figur
Quantum-electrodynamical treatment of second-harmonic generation through phase-conjugate six-wave mixing: Temporal analysis
Environmental factors influencing pipe failures
This report details work carried out under NERC grants NE/M008339/1 and NE/NO13026/1
which were collaborations between the British Geological Survey and Yorkshire Water, with an
additional knowledge transfer component involving Scottish Water and DƔr Cymru Welsh
Water. The work examines whether models developed using environmental, topographical and
geohazard information could complement existing management tools, and increase the
understanding as to how pipe networks of different materials interact with their broader
environment. This can be seen as a first step in identifying ways in which greater resilience could
be built into pipe networks
Pharmacokinetic/pharmacodynamic analysis of adjuvant pegylated interferon α-2b in patients with resected high-risk melanoma
PurposeHigh-dose pegylated interferon α-2b (peginterferon α-2b) significantly decreased disease recurrence in patients with resected stage III melanoma in a clinical study. We investigated the pharmacokinetics (PK) and safety of high-dose peginterferon α-2b in patients with high-risk melanoma.MethodsFor PK analysis, 32 patients received peginterferon α-2b 6 Όg/(kg week) subcutaneously for 8 weeks (induction) then 3 Όg/(kg week) for 4 weeks (maintenance). PK profiles were determined at weeks 1, 8, and 12. Exposure-response relationships between peginterferon α-2b and absolute neutrophil count (ANC) and alanine aminotransferase (ALT) level were also studied.ResultsPeginterferon α-2b was well-absorbed following SC administration, with a median T (max) of 24 h. Mean half-life estimates ranged from 43 to 51 h. The accumulation factor was 1.69 after induction therapy. PK parameters showed moderate interpatient variability. PK profiles were described by a one-compartmental model with first-order absorption and first-order elimination. Toxicity was profiled and was acceptable; observed side effects were similar to those previously described. Dose reduction produced proportional decreases in exposure and predictable effects on ANC in an Imax model; however, a PK/pharmacodynamic (PK/PD) relationship between peginterferon α-2b and ALT could not be established with high precision.ConclusionsPeginterferon α-2b was well-absorbed and sustained exposure to peginterferon α-2b was achieved with the doses tested. These data confirm and extend previous PK observations of peginterferon α-2b in melanoma and solid tumors. Our PK/PD model of exposure and ANC effect provides useful information for prediction of peginterferon α-2b-related hematologic toxicity
The role of marine reserves in achieving sustainable fisheries (One contribution of 15 to a Theme Issue 'Fisheries: a Future?')
Many fishery management tools currently in use have conservation value. They are designed to maintain stocks of commercially important species above target levels. However, their limitations are evident from continuing declines in fish stocks throughout the world. We make the case that to reverse fishery declines, safeguard marine life and sustain ecosystem processes, extensive marine reserves that are off limits to fishing must become part of the management strategy. Marine reserves should be incorporated into modern fishery management because they can achieve many things that conventional tools cannot. Only complete and permanent protection from fishing can protect the most sensitive habitats and vulnerable species. Only reserves will allow the development of natural, extended age structures of target species, maintain their genetic variability and prevent deleterious evolutionary change from the effects of fishing. Species with natural age structures will sustain higher rates of reproduction and will be more resilient to environmental variability. Higher stock levels maintained by reserves will provide insurance against management failure, including risk-prone quota setting, provided the broader conservation role of reserves is firmly established and legislatively protected. Fishery management measures outside protected areas are necessary to complement the protection offered by marine reserves, but cannot substitute for it
Equilibrium Sampling From Nonequilibrium Dynamics
We present some applications of an Interacting Particle System (IPS)
methodology to the field of Molecular Dynamics. This IPS method allows several
simulations of a switched random process to keep closer to equilibrium at each
time, thanks to a selection mechanism based on the relative virtual work
induced on the system. It is therefore an efficient improvement of usual
non-equilibrium simulations, which can be used to compute canonical averages,
free energy differences, and typical transitions paths
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