510 research outputs found
Colloquium: Atomic spin chains on surfaces
In the present Colloquium, we focus on the properties of 1-D magnetic systems
on solid surfaces. From the emulation of 1-D quantum phases to the potential
realization of Majorana edge states, spin chains are unique systems to study.
The advent of scanning tunnelling microscope (STM) based techniques has
permitted us to engineer spin chains in an atom-by-atom fashion via atom
manipulation and to access their spin states on the ultimate atomic scale.
Here, we present the current state of research on spin correlations and
dynamics of atomic spin chains as studied by the STM. After a brief review of
the main properties of spin chains on solid surfaces, we classify spin chains
according to the coupling of their magnetic moments with the holding substrate.
This classification scheme takes into account that the nature and lifetimes of
the spin-chain excitation intrinsically depend on the holding substrate. We
first show the interest of using insulating layers on metals, which generally
results in an increase in the spin state's lifetimes such that their quantized
nature gets evident and they are individually accessible. Next, we show that
the use of semiconductor substrates promises additional control through the
tunable electron density via doping. When the coupling to the substrate is
increased for spin chains on metals, the substrate conduction electron mediated
interactions can lead to emergent exotic phases of the coupled spin
chain-substrate conduction electron system. A particularly interesting example
is furnished by superconductors. Magnetic impurities induce states in the
superconducting gap. Due to the extended nature of the spin chain, the in-gap
states develop into bands that can lead to the emergence of 1-D topological
superconductivity and, consequently to the appearance of Majorana edge states
Live Birth Rates after Active Immunization with Partner Lymphocytes
Although many potential causes have been established for recurrent implantation failure (RIF) and recurrent miscarriage (RM), about 50% of these remain idiopathic. Scientific research is focused on immunological risk factors. In the present study, we aim to evaluate live birth rates after immunization with paternal lymphocytes (lymphocyte immunotherapy (LIT)). This retrospective study consisted of 148 couples with a history of RM and/or RIF. The women underwent immunization with lymphocytes of their respective partners from November 2017 to August 2019. Fifty-five patients (43%) had live births. Stratified by indication (RM, RIF, combined), live birth rates in the RM and the combined group were significantly higher than that in the RIF group (53%, 59% and 33%, respectively, p = 0.02). The difference was especially noticeable during the first 90 days after immunization (conception rate leading to live births: 31%, 23% and 8% for RM, the combined group and RIF, respectively; p = 0.005), while there was no difference between groups during the later follow-up. LIT was associated with high live birth rates, especially in women with recurrent miscarriage. In view of the limited data from randomized studies, LIT cannot be recommended as routine therapy. However, it may be considered in individual cases
Malignant Fibrous Histiocytoma, Aggressive Fibromatosis and Benign Fibrous Tumors Express mRNA for the Metalloproteinase Inducer EMMPRIN and the Metalloproteinases MMP-2 and MT1-MMP
Purpose: Extracellular matrix metalloproteinase inducer (EMMPRIN) has been shown to stimulate fibroblasts to production
of matrix metalloproteinases (MMPs). MMPs comprise a family of proteolytic enzymes implicated in the degradation
of extracellular matrix which has been proposed to be one of the essential steps in tumor invasion and metastases. In the
present study we investigated the expression and location of mRNAs for EMMPRIN, matrix metalloproteinase-2 (MMP-2),
and membrane-type 1 matrix metalloproteinase (MT1-MMP) in mesenchymal tumors with different tendencies to recur or
metastasize
Quantum Approach to a Derivation of the Second Law of Thermodynamics
We re-interprete the microcanonical conditions in the quantum domain as
constraints for the interaction of the "gas-subsystem" under consideration and
its environment ("container"). The time-average of a purity-measure is found to
equal the average over the respective path in Hilbert-space. We then show that
for typical (degenerate or non-degenerate) thermodynamical systems almost all
states within the allowed region of Hilbert-space have a local von
Neumann-entropy S close to the maximum and a purity P close to its minimum,
respectively. Typically thermodynamical systems should therefore obey the
second law.Comment: 4 pages. Accepted for publication in Phys. Rev. Let
Recurrent chromosome 22 deletions in osteoblastoma affect inhibitors of the wnt/beta-catenin signaling pathway.
Osteoblastoma is a bone forming tumor with histological features highly similar to osteoid osteoma; the discrimination between the tumor types is based on size and growth pattern. The vast majority of osteoblastomas are benign but there is a group of so-called aggressive osteoblastomas that can be diagnostically challenging at the histopathological level. The genetic aberrations required for osteoblastoma development are not known and no genetic difference between conventional and aggressive osteoblastoma has been reported. In order to identify recurrent genomic aberrations of importance for tumor development we applied cytogenetic and/or SNP array analyses on nine conventional and two aggressive osteoblastomas. The conventional osteoblastomas showed few or no acquired genetic aberrations while the aggressive tumors displayed heavily rearranged genomes. In one of the aggressive osteoblastomas, three neighboring regions in chromosome band 22q12 were homozygously deleted. Hemizygous deletions of these regions were found in two additional cases, one aggressive and one conventional. In total, 10 genes were recurrently and homozygously lost in osteoblastoma. Four of them are functionally involved in regulating osteogenesis and/or tumorigenesis. MN1 and NF2 have previously been implicated in the development of leukemia and solid tumors, and ZNRF3 and KREMEN1 are inhibitors of the Wnt/beta-catenin signaling pathway. In line with deletions of the latter two genes, high beta-catenin protein expression has previously been reported in osteoblastoma and aberrations affecting the Wnt/beta-catenin pathway have been found in other bone lesions, including osteoma and osteosarcoma
A Study on the Effect of Nudging on Long-Term Boundary Layer Profiles of Wind and Weibull Distribution Parameters in a Rural Coastal Area.
Electrical detection of magnetic skyrmions by non-collinear magnetoresistance
Magnetic skyrmions are localised non-collinear spin textures with high
potential for future spintronic applications. Skyrmion phases have been
discovered in a number of materials and a focus of current research is the
preparation, detection, and manipulation of individual skyrmions for an
implementation in devices. Local experimental characterization of skyrmions has
been performed by, e.g., Lorentz microscopy or atomic-scale tunnel
magnetoresistance measurements using spin-polarised scanning tunneling
microscopy. Here, we report on a drastic change of the differential tunnel
conductance for magnetic skyrmions arising from their non-collinearity: mixing
between the spin channels locally alters the electronic structure, making a
skyrmion electronically distinct from its ferromagnetic environment. We propose
this non-collinear magnetoresistance (NCMR) as a reliable all-electrical
detection scheme for skyrmions with an easy implementation into device
architectures
The role of magnetic anisotropy in the Kondo effect
In the Kondo effect, a localized magnetic moment is screened by forming a
correlated electron system with the surrounding conduction electrons of a
non-magnetic host. Spin S=1/2 Kondo systems have been investigated extensively
in theory and experiments, but magnetic atoms often have a larger spin. Larger
spins are subject to the influence of magnetocrystalline anisotropy, which
describes the dependence of the magnetic moment's energy on the orientation of
the spin relative to its surrounding atomic environment. Here we demonstrate
the decisive role of magnetic anisotropy in the physics of Kondo screening. A
scanning tunnelling microscope is used to simultaneously determine the
magnitude of the spin, the magnetic anisotropy and the Kondo properties of
individual magnetic atoms on a surface. We find that a Kondo resonance emerges
for large-spin atoms only when the magnetic anisotropy creates degenerate
ground-state levels that are connected by the spin flip of a screening
electron. The magnetic anisotropy also determines how the Kondo resonance
evolves in a magnetic field: the resonance peak splits at rates that are
strongly direction dependent. These rates are well described by the energies of
the underlying unscreened spin states.Comment: 14 pages, 4 figures, published in Nature Physic
Atomic spin chain realization of a model for quantum criticality
The ability to manipulate single atoms has opened up the door to constructing
interesting and useful quantum structures from the ground up. On the one hand,
nanoscale arrangements of magnetic atoms are at the heart of future quantum
computing and spintronic devices; on the other hand, they can be used as
fundamental building blocks for the realization of textbook many-body quantum
models, illustrating key concepts such as quantum phase transitions,
topological order or frustration. Step-by-step assembly promises an interesting
handle on the emergence of quantum collective behavior as one goes from one, to
few, to many constituents. To achieve this, one must however maintain the
ability to tune and measure local properties as the system size increases.
Here, we use low-temperature scanning tunneling microscopy to construct arrays
of magnetic atoms on a surface, designed to behave like spin-1/2 XXZ Heisenberg
chains in a transverse field, for which a quantum phase transition from an
antiferromagnetic to a paramagnetic phase is predicted in the thermodynamic
limit. Site-resolved measurements on these finite size realizations reveal a
number of sudden ground state changes when the field approaches the critical
value, each corresponding to a new domain wall entering the chains. We observe
that these state crossings become closer for longer chains, indicating the
onset of critical behavior. Our results present opportunities for further
studies on quantum behavior of many-body systems, as a function of their size
and structural complexity.Comment: published online on 18 Apr 2016 in Nature Physic
Increased mitochondrial activity in a novel IDH1-R132H mutant human oligodendroglioma xenograft model: in situ detection of 2-HG and α-KG
Background: Point mutations in genes encoding NADP+-dependent isocitrate dehydrogenases (especially IDH1) are common in lower grade diffuse gliomas and secondary glioblastomas and occur early during tumor development. The contribution of these mutations to gliomagenesis is not completely understood and research is hampered by the lack of relevant tumor models. We previously described the development of the patient-derived high-grade oligodendroglioma xenograft model E478 that carries the commonly occurring IDH1-R132H mutation. We here report on the analyses of E478 xenografts at the genetic, histologic and metabolic level. Results: LC-MS and in situ mass spectrometric imaging by LESA-nano ESI-FTICR revealed high levels of the proposed oncometabolite D-2-hydroxyglutarate (D-2HG), the product of enzymatic conversion of α-ketoglutarate (α-KG) by IDH1-R132H, in the tumor but not in surrounding brain parenchyma. α-KG levels and total NADP+-dependent IDH activity were similar in IDH1-mutant and -wildtype xenografts, demonstrating that IDH1-mutated cancer cells maintain α-KG levels. Interestingly, IDH1-mutant tumor cells in vivo present with high densities of mitochondria and increased levels of mitochondrial activity as compared to IDH1-wildtype xenografts. It is not yet clear whether this altered mitochondrial activity is a driver or a consequence of tumorigenesis. Conclusions: The oligodendroglioma model presented here is a valuable model for further functional elucidation of the effects of IDH1 mutations on tumor metabolism and may aid in the rational development of novel therapeutic strategies for the large subgroup of gliomas carrying IDH1 mutations
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