39 research outputs found
17O Nuclear Magnetic Resonance Chemical Shift in Oxyhaemoglobin
The 170 chemical shift of oxygen in oxyhaemoglobin is calculated
for two models, one corresponding to the Griffith structure
and the other to the Pauling structure. In both cases the oxygen
resonance is predicted to be several thousand ppm to low field of
the oxygen resonance in water. The shift between the oxygen
nuclei in the Pauling structure is predicted to be at least one
thousand ppm. This large deshielding arises from the local environment
of the oxygen molecule and depends critically on the
splitting of the degenerate it orbitals on complexing
17O Nuclear Magnetic Resonance Chemical Shift in Oxyhaemoglobin
The 170 chemical shift of oxygen in oxyhaemoglobin is calculated
for two models, one corresponding to the Griffith structure
and the other to the Pauling structure. In both cases the oxygen
resonance is predicted to be several thousand ppm to low field of
the oxygen resonance in water. The shift between the oxygen
nuclei in the Pauling structure is predicted to be at least one
thousand ppm. This large deshielding arises from the local environment
of the oxygen molecule and depends critically on the
splitting of the degenerate it orbitals on complexing
Entropy-driven phase transition in a polydisperse hard-rods lattice system
We study a system of rods on the 2d square lattice, with hard-core exclusion.
Each rod has a length between 2 and N. We show that, when N is sufficiently
large, and for suitable fugacity, there are several distinct Gibbs states, with
orientational long-range order. This is in sharp contrast with the case N=2
(the monomer-dimer model), for which Heilmann and Lieb proved absence of phase
transition at any fugacity. This is the first example of a pure hard-core
system with phases displaying orientational order, but not translational order;
this is a fundamental characteristic feature of liquid crystals
A Finite-Volume Version of Aizenman-Higuchi Theorem for the 2d Ising Model
In the late 1970s, in two celebrated papers, Aizenman and Higuchi
independently established that all infinite-volume Gibbs measures of the
two-dimensional ferromagnetic nearest-neighbor Ising model are convex
combinations of the two pure phases. We present here a new approach to this
result, with a number of advantages: (i) We obtain an optimal finite-volume,
quantitative analogue (implying the classical claim); (ii) the scheme of our
proof seems more natural and provides a better picture of the underlying
phenomenon; (iii) this new approach might be applicable to systems for which
the classical method fails.Comment: A couple of typos corrected. To appear in Probab. Theory Relat.
Field
Long-term results from a randomized phase II trial of neoadjuvant combined-modality therapy for locally advanced rectal cancer
Rigorous Probabilistic Analysis of Equilibrium Crystal Shapes
The rigorous microscopic theory of equilibrium crystal shapes has made
enormous progress during the last decade. We review here the main results which
have been obtained, both in two and higher dimensions. In particular, we
describe how the phenomenological Wulff and Winterbottom constructions can be
derived from the microscopic description provided by the equilibrium
statistical mechanics of lattice gases. We focus on the main conceptual issues
and describe the central ideas of the existing approaches.Comment: To appear in the March 2000 special issue of Journal of Mathematical
Physics on Probabilistic Methods in Statistical Physic
Neoadjuvant capecitabine, radiotherapy, and bevacizumab (CRAB) in locally advanced rectal cancer: results of an open-label phase II study
<p>Abstract</p> <p>Background</p> <p>Preoperative capecitabine-based chemoradiation is a standard treatment for locally advanced rectal cancer (LARC). Here, we explored the safety and efficacy of the addition of bevacizumab to capecitabine and concurrent radiotherapy for LARC.</p> <p>Methods</p> <p>Patients with MRI-confirmed stage II/III rectal cancer received bevacizumab 5 mg/kg i.v. 2 weeks prior to neoadjuvant chemoradiotherapy followed by bevacizumab 5 mg/kg on Days 1, 15 and 29, capecitabine 825 mg/m<sup>2 </sup>twice daily on Days 1-38, and concurrent radiotherapy 50.4 Gy (1.8 Gy/day, 5 days/week for 5 weeks + three 1.8 Gy/day), starting on Day 1. Total mesorectal excision was scheduled 6-8 weeks after completion of chemoradiotherapy. Tumour regression grades (TRG) were evaluated on surgical specimens according to Dworak. The primary endpoint was pathological complete response (pCR).</p> <p>Results</p> <p>61 patients were enrolled (median age 60 years [range 31-80], 64% male). Twelve patients (19.7%) had T3N0 tumours, 1 patient T2N1, 19 patients (31.1%) T3N1, 2 patients (3.3%) T2N2, 22 patients (36.1%) T3N2 and 5 patients (8.2%) T4N2. Median tumour distance from the anal verge was 6 cm (range 0-11). Grade 3 adverse events included dermatitis (n = 6, 9.8%), proteinuria (n = 4, 6.5%) and leucocytopenia (n = 3, 4.9%). Radical resection was achieved in 57 patients (95%), and 42 patients (70%) underwent sphincter-preserving surgery. TRG 4 (pCR) was recorded in 8 patients (13.3%) and TRG 3 in 9 patients (15.0%). T-, N- and overall downstaging rates were 45.2%, 73.8%, and 73.8%, respectively.</p> <p>Conclusions</p> <p>This study demonstrates the feasibility of preoperative chemoradiotherapy with bevacizumab and capecitabine. The observed adverse events of neoadjuvant treatment are comparable with those previously reported, but the pCR rate was lower.</p
Optimal designs for rational function regression
We consider optimal non-sequential designs for a large class of (linear and
nonlinear) regression models involving polynomials and rational functions with
heteroscedastic noise also given by a polynomial or rational weight function.
The proposed method treats D-, E-, A-, and -optimal designs in a
unified manner, and generates a polynomial whose zeros are the support points
of the optimal approximate design, generalizing a number of previously known
results of the same flavor. The method is based on a mathematical optimization
model that can incorporate various criteria of optimality and can be solved
efficiently by well established numerical optimization methods. In contrast to
previous optimization-based methods proposed for similar design problems, it
also has theoretical guarantee of its algorithmic efficiency; in fact, the
running times of all numerical examples considered in the paper are negligible.
The stability of the method is demonstrated in an example involving high degree
polynomials. After discussing linear models, applications for finding locally
optimal designs for nonlinear regression models involving rational functions
are presented, then extensions to robust regression designs, and trigonometric
regression are shown. As a corollary, an upper bound on the size of the support
set of the minimally-supported optimal designs is also found. The method is of
considerable practical importance, with the potential for instance to impact
design software development. Further study of the optimality conditions of the
main optimization model might also yield new theoretical insights.Comment: 25 pages. Previous version updated with more details in the theory
and additional example
On the Gibbs states of the noncritical Potts model on Z^2
We prove that all Gibbs states of the q-state nearest neighbor Potts model on
Z^2 below the critical temperature are convex combinations of the q pure
phases; in particular, they are all translation invariant. To achieve this
goal, we consider such models in large finite boxes with arbitrary boundary
condition, and prove that the center of the box lies deeply inside a pure phase
with high probability. Our estimate of the finite-volume error term is of
essentially optimal order, which stems from the Brownian scaling of fluctuating
interfaces. The results hold at any supercritical value of the inverse
temperature.Comment: Minor typos corrected after proofreading. Final version, to appear in
Probab. Theory Relat. Field
An exactly solvable model for the Fermi contact interaction
A model for the Fermi contact interaction is proposed in which the nuclear moment is represented as a magnetized spherical shell of radius r 0 . For a hydrogen-like system thus perturbed, the Schrödinger equation is solvable without perturbation theory by use of the Coulomb Green's function. Approximation formulas are derived in terms of a quantum defect in the Coulombic energy formula. It is shown that the usual Fermi potential cannot be applied beyond first-order perturbation theory.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/46454/1/214_2004_Article_BF00548828.pd