756 research outputs found
High Resolution Study of Magnetic Ordering at Absolute Zero
High fidelity pressure measurements in the zero temperature limit provide a
unique opportunity to study the behavior of strongly interacting, itinerant
electrons with coupled spin and charge degrees of freedom. Approaching the
exactitude that has become the hallmark of experiments on classical critical
phenomena, we characterize the quantum critical behavior of the model,
elemental antiferromagnet chromium, lightly doped with vanadium. We resolve the
sharp doubling of the Hall coefficient at the quantum critical point and trace
the dominating effects of quantum fluctuations up to surprisingly high
temperatures.Comment: 5 pages, 4 figure
Pseudo-contact angle due to superfluid vortices in He
We have investigated spreading of superfluid He on top of polished
MgF and evaporated SiO substrates. Our results show strongly varying
contact angles of 0 - 15 mrad on the evaporated layers. According to our
theoretical calculations, these contact angles can be explained by a spatially
varying distribution of vortex lines, the unpinning velocity of which is
inversely proportional to the liquid depth.Comment: 10 pages, 4 figure
Manipulating coincident charge and spin order with pressure and field in a doped manganite
The onset of charge order occurs simultaneously with the transition from ferromagnetic metal to antiferromagnetic insulator in Nd_(0.05)Sr_(0.5)MnO_3. The application of hydrostatic pressures P≥15 kbar removes the degeneracy, as recorded in both the electrical resistivity and the magnetic susceptibility. The charge-ordered state moves swiftly to higher temperature with increasing pressure at the expense of the ferromagnetic charge liquid, dominating the energetics. An applied magnetic field H suppresses both the pressure-split charge order and the antiferromagnetism, but charge order preferentially, so by H = 2 T the two transitions are reunited. Finally, depinning domains of charge order with electric field deep in the antiferromagnetic insulator permits us to monitor pressure-induced changes in the charge (poly)crystal
Degradation analysis of tribologically loaded carbon nanotubes and carbon onions
Coating laser-patterned stainless-steel surfaces with carbon nanotubes (CNT) or carbon onions (CO) forms a tribological system that
provides effective solid lubrication. Lubricant retention represents the fundamental mechanism of this system, as storing the
particles inside the pattern prevents lubricant depletion in the contact area. In previous works, we used direct laser interference
patterning to create line patterns with three different structural depths on AISI 304 stainless-steel platelets. Electrophoretic
deposition subsequently coated the patterned surfaces with either CNTs or COs. Ball-on-disc friction tests were conducted to study
the effect of structural depth on the solid lubricity of as-described surfaces. The results demonstrated that the shallower the
textures, the lower the coefficient of friction, regardless of the applied particle type. This follow-up study examines the carbon
nanoparticles’ structural degradation after friction testing on substrates patterned with different structural depths (0.24, 0.36, and
0.77 µm). Raman characterization shows severe degradation of both particle types and is used to classify their degradation state
within Ferrari’s three-stage amorphization model. It was further shown that improving CNT lubricity translates into increasing
particle defectivity. This is confirmed by electron microscopy, which shows decreasing crystalline domains. Compared to CNTs, COderived tribofilms show even more substantial structural degradation
Altering crystal growth and annealing in ice-templated scaffolds.
The potential applications of ice-templating porous materials are constantly expanding, especially as scaffolds for tissue engineering. Ice-templating, a process utilizing ice nucleation and growth within an aqueous solution, consists of a cooling stage (before ice nucleation) and a freezing stage (during ice formation). While heat release during cooling can change scaffold isotropy, the freezing stage, where ice crystals grow and anneal, determines the final size of scaffold features. To investigate the path of heat flow within collagen slurries during solidification, a series of ice-templating molds were designed with varying the contact area with the heat sink, in the form of the freeze drier shelf. Contact with the heat sink was found to be critical in determining the efficiency of the release of latent heat within the perspex molds. Isotropic collagen scaffolds were produced with pores which ranged from 90 μm up to 180 μm as the contact area decreased. In addition, low-temperature ice annealing was observed within the structures. After 20 h at -30 °C, conditions which mimic storage prior to lyophilization, scaffold architecture was observed to coarsen significantly. In future, ice-templating molds should consider not only heat conduction during the cooling phase of solidification, but the effects of heat flow during ice growth and annealing.The authors gratefully acknowledge the financial support of the Gates Cambridge Trust, the Newton Trust, and ERC Advanced Grant 320598 3D-E. A.H. held a Daphne Jackson Fellowship funded by the University of Cambridge.This is the final version of the article. It first appeared from Springer via http://dx.doi.org/10.1007/s10853-015-9343-
Follow-up PET/CT of alveolar echinococcosis: Comparison of metabolic activity and immunodiagnostic testing
PURPOSE
To investigate the potential role of follow-up 18F-fluorodeoxyglucose (FDG) positron emission tomography/computed tomography (PET/CT) in therapy control of inoperable patients with alveolar echinococcosis.
MATERIALS AND METHODS
In this single-center retrospective cohort study, 48 PET/CT of 16 patients with confirmed alveolar echinococcosis were analysed. FDG-uptake of the most active echinococcosis manifestation was measured (i.e., maximum standardized uptake value (SUVmax) and in relation to background activity in normal liver tissue (SUVratio)) and compared to immunodiagnostic testing. For clinical patient follow-up, patient demographics, laboratory data, including E. granulosus hydatid fluid (EgHF) antibody units (AU) as well as clinical and treatment information were assessed for all patients at the time of PET/CT, and at the last recorded clinical visit.
RESULTS
Metabolic activity of PET/CT measured in the echinococcosis manifestation was significantly correlated with EgHF AU (p < 0.001). The differences in metabolic activity of echinococcosis manifestations between two consecutive PET/CT examinations of the same patient and differences in EgHF AU in the respective time intervals displayed a significant positive correlation (p = 0.01). A trend for a more rapid decline in SUVratio liver over time was found in patients who stopped benzimidazole therapy versus patients who did not stop therapy (p = 0.059).
CONCLUSION
In inoperable patients with alveolar echinococcosis, the course of metabolic activity in follow-up PET/CT is associated to the course EgHF antibody levels. Both parameters may potentially be used to evaluate the course of the disease and potentially predict the duration of benzimidazole therapy
Highly sensitive piezotronic pressure sensors based on undoped GaAs nanowire ensembles
Semiconducting piezoelectric materials have attracted considerable interest
due to their central role in the emerging field of piezotronics, where the
development of a piezo-potential in response to stress or strain can be used to
tune the band structure of the semiconductor, and hence its electronic
properties. This coupling between piezoelectricity and semiconducting
properties can be readily exploited for force or pressure sensing using
nanowires, where the geometry and unclamped nature of nanowires render them
particularly sensitive to small forces. At the same time, piezoelectricity is
known to manifest more strongly in nanowires of certain semiconductors. Here,
we report the design and fabrication of highly sensitive piezotronic pressure
sensors based on GaAs nanowire ensemble sandwiched between two electrodes in a
back-to-back diode configuration. We analyse the current-voltage
characteristics of these nanowire-based devices in response to mechanical
loading in light of the corresponding changes to the device band structure. We
observe a high piezotronic sensitivity to pressure, of ~7800 meV/MPa. We
attribute this high sensitivity to the nanowires being fully depleted due to
the lack of doping, as well as due to geometrical pressure focusing and current
funneling through polar interfaces
Metal-insulator Crossover Behavior at the Surface of NiS_2
We have performed a detailed high-resolution electron spectroscopic
investigation of NiS and related Se-substituted compounds
NiSSe, which are known to be gapped insulators in the bulk at all
temperatures. A large spectral weight at the Fermi energy of the room
temperature spectrum, in conjunction with the extreme surface sensitivity of
the experimental probe, however, suggests that the surface layer is metallic at
300 K. Interestingly, the evolution of the spectral function with decreasing
temperature is characterized by a continuous depletion of the single-particle
spectral weight at the Fermi energy and the development of a gap-like structure
below a characteristic temperature, providing evidence for a metal-insulator
crossover behavior at the surfaces of NiS and of related compounds. These
results provide a consistent description of the unusual transport properties
observed in these systems.Comment: 12 pages, 3 figure
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