245 research outputs found
Ursell Operators in Statistical Physics III: thermodynamic properties of degenerate gases
We study in more detail the properties of the generalized Beth Uhlenbeck
formula obtained in a preceding article. This formula leads to a simple
integral expression of the grand potential of the system, where the interaction
potential appears only through the matrix elements of the second order Ursell
operator . Our results remain valid for significant degree of degeneracy
of the gas, but not when Bose Einstein (or BCS) condensation is reached, or
even too close from this transition point. We apply them to the study of the
thermodynamic properties of degenerate quantum gases: equation of state,
magnetic susceptibility, effects of exchange between bound states and free
particles, etc. We compare our predictions to those obtained within other
approaches, especially the ``pseudo potential'' approximation, where the real
potential is replaced by a potential with zero range (Dirac delta function).
This comparison is conveniently made in terms of a temperature dependent
quantity, the ``Ursell length'', which we define in the text. This length plays
a role which is analogous to the scattering length for pseudopotentials, but it
is temperature dependent and may include more physical effects than just binary
collision effects; for instance at very low temperatures it may change sign or
increase almost exponentially, an effect which is reminiscent of a precursor of
the BCS pairing transition. As an illustration, numerical results for quantum
hard spheres are given.Comment: 26 pages, 4 figures, LaTeX (amssymb), slight changes to first versio
Congenital Prosopagnosia: Multistage Anatomical and Functional Deficits in Face Processing Circuitry
Face recognition is a primary social skill which depends on a distributed neural network. A pronounced face recognition deficit in the absence of any lesion is seen in congenital prosopagnosia. This study investigating 24 congenital prosopagnosic subjects and 25 control subjects aims at elucidating its neural basis with fMRI and voxel-based morphometry. We found a comprehensive behavioral pattern, an impairment in visual recognition for faces and buildings that spared long-term memory for faces with negative valence. Anatomical analysis revealed diminished gray matter density in the bilateral lingual gyrus, the right middle temporal gyrus, and the dorsolateral prefrontal cortex. In most of these areas, gray matter density correlated with memory success. Decreased functional activation was found in the left fusiform gyrus, a crucial area for face processing, and in the dorsolateral prefrontal cortex, whereas activation of the medial prefrontal cortex was enhanced. Hence, our data lend strength to the hypothesis that congenital prosopagnosia is explained by network dysfunction and suggest that anatomic curtailing of visual processing in the lingual gyrus plays a substantial role. The dysfunctional circuitry further encompasses the fusiform gyrus and the dorsolateral prefrontal cortex, which may contribute to their difficulties in long-term memory for complex visual information. Despite their deficits in face identity recognition, processing of emotion related information is preserved and possibly mediated by the medial prefrontal cortex. Congenital prosopagnosia may, therefore, be a blueprint of differential curtailing in networks of visual cognition
Bacterial diversity and community composition in the chemocline of the meromictic alpine Lake Cadagno as revealed by 16S rDNA analysis
Using different techniques of molecular biology we investigated the bacterial diversity of the chemocline of the meromictic Lake Cadagno. Cloning of a total community 16S rDNA PCR product and subsequent screening with a combination of amplified ribosomal DNA restriction analysis and temporal temperature gradient gel electrophoresis (TTGE) analysis revealed that 30 of 47 randomly selected clones were unique. Partial sequencing and comparative analysis indicated a high bacterial diversity dominated by the γ-Proteobacteria (33.3%). Most of these rDNA clone sequences were not closely related to any 16S rDNA sequence in the database. In a second approach, the TTGE pattern from an environmental sample was compared with the migration of the cloned 16S rDNA fragments. Four clone types were identified on the environmental pattern by excising and sequencing comigrating bands, three of which were well represented in the library: two Chromatiaceae species and one sequence affiliated with the Desulfobulbus assemblage. Using the fluorescent in situ hybridization technique we essentially confirmed the results of the cloning experiments and the TTGE analysi
Effective interaction between molecules in the BEC regime of a superfluid Fermi gas
We investigate the effective interaction between Cooper-pair molecules in the
st rong-coupling BEC regime of a superfluid Fermi gas with a Feshbach
resonance. Our work uses a path integral formulation and a renormalization
group (RG) analy sis of fluctuations in a single-channel model. We show that a
physical cutoff en ergy originating from the finite molecular
binding energy is the key to understanding the interaction between molecules in
the BEC regime. Our work t hus clarifies recent results by showing that is a {\it ba re} molecular scattering length while is the low energy molecular scattering length
renormalized to include high-energy scat tering up to (here is the scattering length between Fermi atoms). We also include many-body
effects at finite temperatures. We find that is strongly dependent
on temperature, vanishing at , consistent with the earlier Bose gas
results of Bijlsma and Stoof.Comment: 10 pages, 3 figure
Conserving Gapless Mean-Field Theory for Bose-Einstein Condensates
We formulate a conserving gapless mean-field theory for Bose-Einstein
condensates on the basis of a Luttinger-Ward thermodynamic functional. It is
applied to a weakly interacting uniform gas with density and s-wave
scattering length to clarify its fundamental thermodynamic properties. It
is found that the condensation here occurs as a first-order transition. The
shift of the transition temperature from the ideal-gas result
is positive and given to the leading order by , in agreement with a couple of previous estimates. The theory is
expected to form a new theoretical basis for trapped Bose-Einstein condensates
at finite temperatures.Comment: Minor errors remove
Long-term organic matter application reduces cadmium but not zinc concentrations in wheat
Wheat is a staple food crop and a major source of both the essential micronutrient zinc (Zn) and the toxic heavy metal cadmium (Cd) for humans. Since Zn and Cd are chemically similar, increasing Zn concentrations in wheat grains (biofortification), while preventing Cd accumulation, is an agronomic challenge. We used two Swiss agricultural long-term field trials, the “Dynamic-Organic-Conventional System Comparison Trial” (DOK) and the “Zurich Organic Fertilization Experiment” (ZOFE), to investigate the impact of long-term organic, mineral and combined fertilizer inputs on total and phytoavailable concentrations of soil Zn and Cd and their accumulation in winter wheat ( L.). “Diffusive gradients in thin films” (DGT) and diethylene-triaminepentaacetic acid (DTPA) extraction were used as proxies for plant available soil metals. Compared to unfertilized controls, long-term organic fertilization with composted manure or green waste compost led to higher soil organic carbon, cation exchange capacity and pH, while DGT-available Zn and Cd concentrations were reduced. The DGT method was a strong predictor of shoot and grain Cd, but not Zn concentrations. Shoot and grain Zn concentrations correlated with DTPA-extractable and total soil Zn concentrations in the ZOFE, but not the DOK trial. Long-term compost fertilization led to lower accumulation of Cd in wheat grains, but did not affect grain Zn. Therefore, Zn/Cd ratios in the grains increased. High Zn and Cd inputs with organic fertilizers and high Cd inputs with phosphate fertilizers led to positive Zn and Cd mass balances when taking into account atmospheric deposition and fertilizer inputs. On the other hand, mineral fertilization led to the depletion of soil Zn due to higher yields and thus higher Zn exports than under organic management. The study supports the use of organic fertilizers for reducing Cd concentrations of wheat grains in the long-term, given that the quality of the fertilizers is guaranteed
Transition Temperature of a Uniform Imperfect Bose Gas
We calculate the transition temperature of a uniform dilute Bose gas with
repulsive interactions, using a known virial expansion of the equation of
state. We find that the transition temperature is higher than that of an ideal
gas, with a fractional increase K_0(na^3)^{1/6}, where n is the density and a
is the S-wave scattering length, and K_0 is a constant given in the paper. This
disagrees with all existing results, analytical or numerical. It agrees exactly
in magnitude with a result due to Toyoda, but has the opposite sign.Comment: Email correspondence to [email protected] ; 2 pages using REVTe
Local recurrence at the site of the Lone Star device through implantation of exfoliated cells during local excision for early rectal cancer:A case report
Introduction: Invasive procedures for colorectal cancer can cause iatrogenic tumor cell seeding. Implantation of these exfoliated cells in the surrounding tissue can result in locoregional cancer recurrence. This has been described in endoscopic procedures and major surgical resections, however recurrence in iatrogenic lesions of the anal canal during minimal invasive rectal surgery has not been shown in literature yet. This is the first reported case of recurrent rectal cancer that developed into an anal metastasis at the site where hooks of the Lone Star Retractor disrupted the epithelial lining of the anal canal during a local excision of early rectal cancer using TAMIS. Presentation of case: A 57 year old male was diagnosed with a high risk early stage rectal adenocarcinoma. He was treated with transanal minimally invasive surgery (TAMIS) with the use of a Lone Star retractor and he received subsequent chemo-radiotherapy. 23 months later the patient developed a bleeding mass bulging out of the anus. A true cut and incision biopsy was performed and the pathology report revealed localization of adenocarcinoma at the anal canal which was similar to the earlier diagnosed rectal carcinoma. The patient underwent an abdominal perineal resection and left-sided lymph node dissection. Discussion and conclusion: This shows that local recurrence through implantation of exfoliated tumor cells can occur in iatrogenic lesions of the anal canal not only in major but also in minimal invasive rectal surgery. Careful tissue handling and rectal washout may reduce the chance of this implantation metastasis.</p
Transition temperature of a dilute homogeneous imperfect Bose gas
The leading-order effect of interactions on a homogeneous Bose gas is
theoretically predicted to shift the critical temperature by an amount
\Delta\Tc = # a_{scatt} n^{1/3} T_0 from the ideal gas result T_0, where
a_{scatt} is the scattering length and n is the density. There have been
several different theoretical estimates for the numerical coefficient #. We
claim to settle the issue by measuring the numerical coefficient in a lattice
simulation of O(2) phi^4 field theory in three dimensions---an effective theory
which, as observed previously in the literature, can be systematically matched
to the dilute Bose gas problem to reproduce non-universal quantities such as
the critical temperature. We find # = 1.32 +- 0.02.Comment: 4 pages, submitted to Phys. Rev. Lett; minor changes due to
improvement of analysis in the longer companion pape
Local recurrence at the site of the Lone Star device through implantation of exfoliated cells during local excision for early rectal cancer:A case report
Introduction: Invasive procedures for colorectal cancer can cause iatrogenic tumor cell seeding. Implantation of these exfoliated cells in the surrounding tissue can result in locoregional cancer recurrence. This has been described in endoscopic procedures and major surgical resections, however recurrence in iatrogenic lesions of the anal canal during minimal invasive rectal surgery has not been shown in literature yet. This is the first reported case of recurrent rectal cancer that developed into an anal metastasis at the site where hooks of the Lone Star Retractor disrupted the epithelial lining of the anal canal during a local excision of early rectal cancer using TAMIS. Presentation of case: A 57 year old male was diagnosed with a high risk early stage rectal adenocarcinoma. He was treated with transanal minimally invasive surgery (TAMIS) with the use of a Lone Star retractor and he received subsequent chemo-radiotherapy. 23 months later the patient developed a bleeding mass bulging out of the anus. A true cut and incision biopsy was performed and the pathology report revealed localization of adenocarcinoma at the anal canal which was similar to the earlier diagnosed rectal carcinoma. The patient underwent an abdominal perineal resection and left-sided lymph node dissection. Discussion and conclusion: This shows that local recurrence through implantation of exfoliated tumor cells can occur in iatrogenic lesions of the anal canal not only in major but also in minimal invasive rectal surgery. Careful tissue handling and rectal washout may reduce the chance of this implantation metastasis.</p
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