534 research outputs found
Rotational Symmetry Breaking in Sodium Doped Cuprates
For reasonable parameters a hole bound to a Na^{+} acceptor in
Ca_{2-x}Na_{x}CuO_{2}Cl_{2} has a doubly degenerate ground state whose
components can be represented as states with even (odd) reflection symmetry
around the x(y) -axes. The conductance pattern for one state is anisotropic as
the tip of a tunneling microscope scans above the Cu-O-Cu bonds along the
x(y)-axes. This anisotropy is pronounced at lower voltages but is reduced at
higher voltages. Qualitative agreement with recent experiments leads us to
propose this effect as an explanation of the broken local rotational symmetry.Comment: 10 pages, 4 figure
Efficacy of B-cell-targeted therapy with rituximab in patients with rheumatoid arthritis.
BACKGROUND: An open-label study indicated that selective depletion of B cells with the use of rituximab led to sustained clinical improvements for patients with rheumatoid arthritis. To confirm these observations, we conducted a randomized, double-blind, controlled study. METHODS: We randomly assigned 161 patients who had active rheumatoid arthritis despite treatment with methotrexate to receive one of four treatments: oral methotrexate (> or =10 mg per week) (control); rituximab (1000 mg on days 1 and 15); rituximab plus cyclophosphamide (750 mg on days 3 and 17); or rituximab plus methotrexate. Responses defined according to the criteria of the American College of Rheumatology (ACR) and the European League against Rheumatism (EULAR) were assessed at week 24 (primary analyses) and week 48 (exploratory analyses). RESULTS: At week 24, the proportion of patients with 50 percent improvement in disease symptoms according to the ACR criteria, the primary end point, was significantly greater with the rituximab-methotrexate combination (43 percent, P=0.005) and the rituximab-cyclophosphamide combination (41 percent, P=0.005) than with methotrexate alone (13 percent). In all groups treated with rituximab, a significantly higher proportion of patients had a 20 percent improvement in disease symptoms according to the ACR criteria (65 to 76 percent vs. 38 percent, P< or =0.025) or had EULAR responses (83 to 85 percent vs. 50 percent, P< or =0.004). All ACR responses were maintained at week 48 in the rituximab-methotrexate group. The majority of adverse events occurred with the first rituximab infusion: at 24 weeks, serious infections occurred in one patient (2.5 percent) in the control group and in four patients (3.3 percent) in the rituximab groups. Peripheral-blood immunoglobulin concentrations remained within normal ranges. CONCLUSIONS: In patients with active rheumatoid arthritis despite methotrexate treatment, a single course of two infusions of rituximab, alone or in combination with either cyclophosphamide or continued methotrexate, provided significant improvement in disease symptoms at both weeks 24 and 48
Detection of minimal residual disease in acute lymphoblastic leukemia
Acute lymphoblastic leukemia (ALL) represents the most frequent malignancy in
childhood. Last decades brought enormous progress in ALL treatment and in the
understanding of ALL biology (see Chapter 1.1 ), but still 20 to 30% of children suffer
from relapse and many of them will ultimately die of disease progression. The currently
used cytomorphological (microscopic) techniques can only detect 1 to 5% of
malignant cells, which is not sufficiently sensitive for identification of patients who are
prone to relapse and who might be rescued by treatment intensification. During the
past 15 years several approaches have been developed for detection of much lower
numbers of malignant cells, i.e. for detection of minimal residual disease (MRD) in
various hematopoietic malignancies (see Chapter 1.2). Monitoring of MRD with sensitivities
of 1 Q-4 to 1 o-6 (i.e. one malignant cell within the background of 104 to 106
normal cells) has significantly higher prognostic value than conventional cytomorphological
techniques and other clinical parameters at diagnosis and is therefore currently
implemented into clinical practice in several hematopoietic malignancies,
including ALL.
In childhood ALL, detection of MRD most frequently relies on patient-specific
immunoglobulin (lg) and T-cell receptor (TCR) gene rearrangements as molecular
markers for PCR studies. The junctional regions of rearranged lg and TCR genes are
unique "fingerprint-like" sequences, which are assumed to be different in each lymphoid
cell and thus also in each lymphoid malignancy. They can be easily identified
and characterized for instance by using heteroduplex PCR analysis (see Chapter
2.2) and direct sequencing.
This thesis aimed at detailed evaluation of lg and TCR gene rearrangements in
ALL with regard to the following aspects:
-characterization of lg/TCR gene rearrangements patterns in precursor-BALL
and T-ALL;
- immunobiological differences between malignant and normal lymphoid cells;
-stability of clonal lg/TCR gene rearrangements at relapse of ALL;
-applicability of lg/TCR gene rearrangements as PCR targets for detection of
MRD.
Virtually all precursor-B-ALL (96%) have rearranged lg heavy chain (/GH) genes.
In most cases (80-90%) this concerns complete VH-DH-JH rearrangements on at
least one allele. Incomplete DH-JH rearrangements could be identified in 22% of
patients, being the sole /GH gene rearrangements in only 5% of patients (see
Chapter 2.3). Most precursor-B-ALL contain lg kappa (/GK) light chain gene
rearrangements (30%) or deletions (50%); 20% of precursor-B-ALL cases even have
lg lambda (IGL) gene rearrangements. Deletions in the IGK genes are predominantly
mediated via the IGK deleting element (Kde) sequence. Such Kde rearrangements
occur in 50% of precursor-B-ALL case
Controlling shot noise in double-barrier magnetic tunnel junctions
We demonstrate that shot noise in Fe/MgO/Fe/MgO/Fe double-barrier magnetic
tunnel junctions is determined by the relative magnetic configuration of the
junction and also by the asymmetry of the barriers. The proposed theoretical
model, based on sequential tunneling through the system and including spin
relaxation, successfully accounts for the experimental observations for bias
voltages below 0.5V, where the influence of quantum well states is negligible.
A weak enhancement of conductance and shot noise, observed at some voltages
(especially above 0.5V), indicates the formation of quantum well states in the
middle magnetic layer. The observed results open up new perspectives for a
reliable magnetic control of the most fundamental noise in spintronic
structures.Comment: 8 pages, 4 figure
Interaction of a Magnetic Impurity with Strongly Correlated Conduction Electrons
We consider a magnetic impurity which interacts by hybridization with a
system of strongly correlated conduction electrons. The latter are described by
a Hubbard Hamiltonian. By means of a canconical transformation the charge
degrees of freedom of the magnetic impurity are eliminated. The resulting
effective Hamiltonian is investigated and various limiting cases
are considered. If the Hubbard interaction between the conduction electrons
is neglected reduces to a form obtained by the Schrieffer-Wolff
transformation, which is essentially the Kondo Hamiltonian. If is large and
the correlations are strong is changed. One modification concerns
the coefficient of the dominant exchange coupling of the magnetic impurity with
the nearest lattice site. When the system is hole doped, there is also an
antiferromagnetic coupling to the nearest neighbors of that site involving
additionally a hole. Furthermore, it is found that the magnetic impurity
attracts a hole. In the case of electron doping, double occupancies are
repelled by the impurity. In contrast to the hole-doped case, we find no
magnetic coupling which additionally involves a doubly occupied site.Comment: 16 pages, Revtex 3.
Anomalous Spin and Charge Dynamics of the 2D t-J Model at low doping
We present an exact diagonalization study of the dynamical spin and density
correlation function of the 2D t-J model for hole doping < 25%. Both
correlation functions show a remarkably regular, but completely different
scaling behaviour with both hole concentration and parameter values: the
density correlation function is consistent with that of bosons corresponding to
the doped holes and condensed into the lowest state of the noninteracting band
of width 8t, the spin correlation function is consistent with Fermions in a
band of width J. We show that the spin bag picture gives a natural explanation
for this unusual behaviour.Comment: Revtex-file, 4 PRB pages + 5 figures attached as uu-encoded ps-files
Hardcopies of figures (or the entire manuscript) can also be obtained by
e-mailing to: [email protected]
Comparative analysis of Ig and TCR gene rearrangements at diagnosis and at elapse of childhood precursor-B–ALL provides improved strategies for selection of stable PCR targets for monitoring of minimal residual disease
Immunoglobulin (Ig) and T-cell receptor (TCR) gene rearrangements are excellent patient-specific polymerase chain reaction (PCR) targets for detection of minimal residual disease (MRD) in acute lymphoblastic leukemia (ALL), but they might be unstable during the disease course.
Therefore, we performed detailed molecula
Spin and Charge Texture around In-Plane Charge Centers in the CuO_2 planes
Recent experiments on La_2Cu_{1-x}Li_xO_4 show that although the doped holes
remain localized near the substitutional Li impurities, magnetic order is
rapidly suppressed. An examination of the spin texture around a bound hole in a
CuO_2 plane shows that the formation of a skyrmion is favored in a wide range
of parameters, as was previously proposed in the context of Sr doping. The spin
texture may be observable by elastic diffuse neutron scattering, and may also
have a considerable effect on NMR lineshapes.Comment: 4 pages, postscript file, hardcopy available upon request, to appear
in PR
Green Function Monte Carlo with Stochastic Reconfiguration: an effective remedy for the sign problem disease
A recent technique, proposed to alleviate the ``sign problem disease'', is
discussed in details. As well known the ground state of a given Hamiltonian
can be obtained by applying the imaginary time propagator to a
given trial state for large imaginary time and sampling
statistically the propagated state . However
the so called ``sign problem'' may appear in the simulation and such
statistical propagation would be practically impossible without employing some
approximation such as the well known ``fixed node'' approximation (FN). This
method allows to improve the FN dynamic with a systematic correction scheme.
This is possible by the simple requirement that, after a short imaginary time
propagation via the FN dynamic, a number of correlation functions can be
further constrained to be {\em exact} by small perturbation of the FN
propagated state, which is free of the sign problem. By iterating this scheme
the Monte Carlo average sign, which is almost zero when there is sign problem,
remains stable and finite even for large . The proposed algorithm is
tested against the exact diagonalization results available on finite lattice.
It is also shown in few test cases that the dependence of the results upon the
few parameters entering the stochastic technique can be very easily controlled,
unless for exceptional cases.Comment: 44 pages, RevTeX + 5 encaplulated postscript figure
Hole dynamics in generalized spin backgrounds in infinite dimensions
We calculate the dynamical behaviour of a hole in various spin backgrounds in
infinite dimensions, where it can be determined exactly. We consider hypercubic
lattices with two different types of spin backgrounds. On one hand we study an
ensemble of spin configurations with an arbitrary spin probability on each
sublattice. This model corresponds to a thermal average over all spin
configurations in the presence of staggered or uniform magnetic fields. On the
other hand we consider a definite spin state characterized by the angle between
the spins on different sublattices, i.e a classical spin system in an external
magnetic field. When spin fluctuations are considered, this model describes the
physics of unpaired particles in strong coupling superconductors.Comment: Accepted in Phys. Rev. B. 18 pages of text (1 fig. included) in Latex
+ 2 figures in uuencoded form containing the 2 postscripts (mailed
separately
- …