335 research outputs found
Facial nerve schwannoma presenting as mixed hearing loss, tinnitus, and dizziness
Introduction: Facial nerve involvement in skull base tumors is quite a common finding. However, facial nerve tumors are rare. Facial nerve schwannomas can be observed in 75% of facial nerve tumors. They are slowly growing, benign tumors that can arise from any segment of the facial nerve—from the cerebellopontine angle to the parotid gland. The most common clinical presentation in patients with an intratemporal schwannoma is a slowly progressing facial nerve dysfunction. Less frequently, a fluctuating or a sudden facial nerve weakness can be seen. Hearing loss, tinnitus, and dizziness can also be observed in facial nerve schwannomas. Hearing loss can be conductive, sensorineural or mixed, depending on the size and site of the tumor that can extend into the middle ear or erode the cochlea. Tumors of the internal auditory canal or of the cerebellopontine angle usually lead to a retrocochlear sensorineural hearing loss.Case Presentation: The authors present the case of a 19-year-old man suffering from a left-sided hearing loss, tinnitus and dizziness without any facial nerve dysfunction.Results: The patient underwent computed tomography (CT) scan and magnetic resonance imaging (MRI) with gadolinium to investigate the middle ear and internal auditory canal. A left facial nerve schwannoma, involving the geniculated ganglion, was diagnosed.Conclusion: Even if the most common symptoms of facial nerve schwannomas are facial nerve-related symptoms, we should always keep in mind that hearing-related and equilibrium-related symptoms can be the first presenting symptoms
Thermal Lens Measurements of Thermal Expansivity in Thermosensitive Polymer Solutions
The weak absorption of a laser beam generates in a fluid an inhomogeneous refractive
index profile acting as a negative lens. This self-effect on beam propagation, known as Thermal
Lensing (TL), is extensively exploited in sensitive spectroscopic techniques, and in several all-optical
methods for the assessment of thermo-optical properties of simple and complex fluids. Using the
Lorentz–Lorenz equation, we show that the TL signal is directly proportional to the sample thermal
expansivity a, a feature allowing minute density changes to be detected with high sensitivity in a tiny
sample volume, using a simple optical scheme. We took advantage of this key result to investigate the
compaction of PniPAM microgels occurring around their volume phase transition temperature, and
the temperature-driven formation of poloxamer micelles. For both these different kinds of structural
transitions, we observed a significant peak in the solute contribution to a, indicating a decrease in the
overall solution density—rather counterintuitive evidence that can nevertheless be attributed to the
dehydration of the polymer chains. Finally, we compare the novel method we propose with other
techniques currently used to obtain specific volume changes
Effect of Scatterering on Coherent Anti-Stokes Raman Scattering (CARS) signals
We develop a computational framework to examine the factors responsible for
scattering-induced distortions of coherent anti-Stokes Raman scattering (CARS)
signals in turbid samples. We apply the Huygens-Fresnel Wave-based Electric
Field Superposition (HF-WEFS) method combined with the radiating dipole
approximation to compute the effects of scattering-induced distortions of focal
excitation fields on the far-field CARS signal. We analyze the effect of
spherical scatterers, placed in the vicinity of the focal volume, on the CARS
signal emitted by different objects (2{\mu}m diameter solid sphere, 2{\mu}m
diameter myelin cylinder and 2{\mu}m diameter myelin tube). We find that
distortions in the CARS signals arise not only from attenuation of the focal
field but also from scattering-induced changes in the spatial phase that
modifies the angular distribution of the CARS emission. Our simulations further
show that CARS signal attenuation can be minimized by using a high numerical
aperture condenser. Moreover, unlike the CARS intensity image, CARS images
formed by taking the ratio of CARS signals obtained using x- and y-polarized
input fields is relatively insensitive to the effects of spherical scatterers.
Our computational framework provide a mechanistic approach to characterizing
scattering-induced distortions in coherent imaging of turbid media and may
inspire bottom-up approaches for adaptive optical methods for image correction.Comment: 15 pages, 7 figure
Optothermal crystallization of hard spheres in an effective bidimensional geometry
Using colloids effectively confined in two dimensions by a cell with a thickness comparable to the particle size, we investigate the nucleation and growth of crystallites induced by locally heating the solvent with a near-infrared laser beam. The particles, which are "thermophilic," move towards the laser spot solely because of thermophoresis with no convection effects, forming dense clusters whose structure is monitored using two order parameters that gauge the local density and the orientational ordering. We find that ordering takes place when the cluster reaches an average surface density that is still below the upper equilibrium limit for the fluid phase of hard disks, meaning that we do not detect any sign of a proper "two-stage" nucleation from a glass or a polymorphic crystal structure. The crystal obtained at late growth stage displays a remarkable uniformity with a negligible amount of defects, arguably because the incoming particles diffuse, bounce, and displace other particles before settling at the crystal interface. This "fluidization" of the outer crystal edge may resemble the surface enhanced mobility giving rise to ultra-stable glasses by physical vapor deposition
First-Order Phase Transition in a Quantum Hall Ferromagnet
The single-particle energy spectrum of a two-dimensional electron gas in a
perpendicular magnetic field consists of equally-spaced spin-split Landau
levels, whose degeneracy is proportional to the magnetic field strength. At
integer and particular fractional ratios between the number of electrons and
the degeneracy of a Landau level (filling factors n) quantum Hall effects
occur, characterised by a vanishingly small longitudinal resistance and
quantised Hall voltage. The quantum Hall regime offers unique possibilities for
the study of cooperative phenomena in many-particle systems under
well-controlled conditions. Among the fields that benefit from quantum-Hall
studies is magnetism, which remains poorly understood in conventional material.
Both isotropic and anisotropic ferromagnetic ground states have been predicted
and few of them have been experimentally studied in quantum Hall samples with
different geometries and filling factors. Here we present evidence of
first-order phase transitions in n = 2 and 4 quantum Hall states confined to a
wide gallium arsenide quantum well. The observed hysteretic behaviour and
anomalous temperature dependence in the longitudinal resistivity indicate the
occurrence of a transition between the two distinct ground states of an Ising
quantum-Hall ferromagnet. Detailed many-body calculations allowed the
identification of the microscopic origin of the anisotropy field
Self-assembly and electron-beam-induced direct etching of suspended graphene nanostructures
We report on suspended single-layer graphene deposition by a
transfer-printing approach based on polydimethylsiloxane stamps. The transfer
printing method allows the exfoliation of graphite flakes from a bulk graphite
sample and their residue-free deposition on a silicon dioxide substrate. This
deposition system creates a blistered graphene surface due to strain induced by
the transfer process itself. Single-layer-graphene deposition and its
"blistering" on the substrate are demonstrated by a combination of Raman
spectroscopy, scanning electron microscopy and atomic-force microscopy
measurements. Finally, we demonstrate that blister-like suspended graphene are
self-supporting single-layer structures and can be flattened by employing a
spatially-resolved direct-lithography technique based on electron-beam induced
etching.Comment: 17 pages, 5 figure
The Influence of Graphene Curvature on Hydrogen Adsorption: Towards Hydrogen Storage Devices
The ability of atomic hydrogen to chemisorb on graphene makes the latter a
promising material for hydrogen storage. Based on scanning tunneling microscopy
techniques, we report on site-selective adsorption of atomic hydrogen on
convexly curved regions of monolayer graphene grown on SiC(0001). This system
exhibits an intrinsic curvature owing to the interaction with the substrate. We
show that at low coverage hydrogen is found on convex areas of the graphene
lattice. No hydrogen is detected on concave regions. These findings are in
agreement with theoretical models which suggest that both binding energy and
adsorption barrier can be tuned by controlling the local curvature of the
graphene lattice. This curvature-dependence combined with the known graphene
flexibility may be exploited for storage and controlled release of hydrogen at
room temperature making it a valuable candidate for the implementation of
hydrogen-storage devices
Manual sampling and tank size effects on the calibration curve of plot sediment storage tanks
In many experimental soil erosion plots, runoff is collected and carried by a conveyance system to a sequence of
storage tanks. If the soil loss is measured by collecting, after mixing, samples of the stored suspension, then a calibration curve between the actual mean concentration (C) and the measured concentration (Cm) in the storage tank occurs. The aim of this article was to evaluate experimentally the factors affecting the relationship between C and Cm. For a sandy loam soil, the replicated measurements of Cm (20 samples) for two values of the actual concentration (C = 5 and 25 g/L) showed that the variability of the measurements of Cm is low and confirmed the reliability of a calibration curve obtained by a single series of runs. Results from experiments carried out with a clay soil to compare the calibration curves obtained by four field workers suggested that the maximum uncertainty in the soil loss measurement due to the choice of the calibration curve should not exceed 100% of the true value. Moreover, the slope of the calibration curve was independent of both the water level in the tank and the field worker. Finally, a comparison among the calibration curves of a prototype tank and some model tanks was carried out for both a sandy loam and a clay soil in order to establish a scaled−up relationship among tanks of different size. Soil−specific and theoretically based scaled−up relationships were deduced
Large thermal biasing of individual gated nanostructures
We demonstrate a novel nanoheating scheme that yields very large and uniform
temperature gradients up to about 1K every 100nm, in an architecture which is
compatible with the field-effect control of the nanostructure under test. The
temperature gradients demonstrated largely exceed those typically obtainable
with standard resistive heaters fabricated on top of the oxide layer. The
nanoheating platform is demonstrated in the specific case of a short-nanowire
device.Comment: 6 pages, 6 figure
- …