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At least 343 records · Page 19Linked to original sources
PubMed2000

Mirror movements complicate interpretation of cerebral activation changes during recovery from subcortical infarction.

In recovered stroke patients, performance of motor tasks with the affected limb has been reported to activate cortical areas ipsilateral to the affected side. The better to determine the causal role these areas play in recovery of motor function, we assessed cerebral activation during motor activity longitudinally after hemiparesis due to cerebral infarction. A secondary goal was to ascertain the relation between mirror movements and activation ipsilateral to motor activity. Positron emission tomography with oxygen-15 water measured regional cerebral blood flow during wrist movement early and late in the course of recovery from hemiparesis. Surface electromyography recorded muscular activity, and computer-assisted video analysis quantified movement during the scans. Mirror movements, movements contralateral to the instructed movement of the hemiparetic arm, were often seen. Activation of motor areas in the hemisphere ipsilateral to the affected limb roughly correlated with presence of mirror movements. Other changes in cerebral activation were small, when the task was controlled for rate, but high-rate-specific recruitment of ipsilateral cortical areas occurred in one case. However, the common occurrence of mirror movements, particularly with effortful tasks, complicates interpretation of data regarding the role of the ipsilateral hemisphere in recovery.

Aged↗
PubMed2006

T-cell lymphoproliferative disorder of hand-mirror cell morphology presenting in an eosinophilic loculated peritoneal effusion, with omental "caking".

BACKGROUND: Cells with "hand mirror" morphology have not, to the best of our knowledge, been described in a primary effusion sample. This paper describes a case of T-cell lymphoma with eosinophilia in a patient with suspected peritoneal carcinomatosis. Rarely, a T-cell lymphoproliferative process may mimic primary peritoneal carcinomatosis, clinically suggested by a presentation in CT imaging of omental caking with bilateral massive loculated effusions in a patient without lymphadenopathy or splenomegaly. METHODS: A 60 year old caucasian male presented with vague abdominal discomfort and increasing abdominal girth. Computed tomography showed a two centimeter thick omental cake and a small loculated effusion. The clinical presentation and imaging findings were most consistent with peritoneal carcinomatosis. Cytologic evaluation of the effusion was undertaken for diagnostic study. RESULTS: Rapid intraprocedural interpretation of the effusion sample showed a monomorphic population of cells with "hand-mirror" cell morphology exhibiting cytoplasmic extensions (uropodia) with 3-5 course dark cytoplasmic granules and a rim of vacuolated cytoplasm capping the opposing "mirror head" side. These cells were seen within a background of mature eosinophils. Flow cytometric evaluation of the ascites fluid demonstrated an atypical T-cell population with the following immunophenotype: CD2-, CD3+, CD4-, CD5-, CD7-, CD8+, CD56+. T-cell receptor (TCR) gene rearrangement was positive for clonal TCR-gamma gene rearrangement, supporting the diagnosis of a T-lymphoproliferative disorder. CONCLUSION: A T-cell lymphoproliferative process may present with "hand mirror" morphology in an effusion sample. These cells may show polar cytoplasmic vacuolization and 3-5 course granules within the "handle" of these unique cells. Cytoplasm shows peripheral constriction around the nucleus.

Journal Article↗
PubMed1985

Mirror movement asymmetries in congenital hemiparesis: the inhibition hypothesis revisited.

Mirror movements are seen in normal children in the first decade. The movements persist after age 10 in patients with congenital hemiparesis. At first, mirror movements are more prominent in the good hand (when the impaired hand attempts a unimanual task), but after age 10, mirroring diminishes in the good hand, and these movements are equally prominent in good and impaired hands. Maturational changes in callosally mediated inhibition of uncrossed motor pathways and reorganizational changes of the pyramidal motor system after early unilateral brain injury explain these age-dependent changes in asymmetries of mirror movements.

Adolescent↗
PubMed2006

[Population genetic variation and structure analysis on five populations of mirror carp Cyprinus carpio L. using microsatellites].

In this paper, population genetic variability and genetic structure of five populations of an important cultivation species, mirror carp (Cyprinus carpio L.) were analyzed using 30 microsatellite loci. The observed (Ho) and expected (He) heterozygosity values, polymorphic information content (PIC) and number of effective alleles (Ae) were all determined. The genetic similarity coefficient and Nei's standard genetic distance were computed based on the allele frequencies. The Hardy-Weinberg equilibrium was checked by chi2 test. Genetic differentiation and hierarchical partition of genetic diversity were evaluated by FST and Nm. A dendrogram was constructed based on UPGMA methods using PHYLIP software package supported by a bootstrap value of 91.0%. Totally 7,083 fragments were procured. Their lengths were from 102 bp to 446 bp. For each locus, 1-16 alleles were amplified, adding up to 356 alleles in all the 5 populations. We found the genetic variability level was relatively high in all five populations, as shown by Ae = 1.07-2.30, He= 0.70-0.78 and PIC=0.69-0.75, respectively. The genetic similarity coefficients were all above 0.52, indicating their close genetic relationships. The UPGMA phylogenetic tree showed mirror carps sampled from Donggang, Fengcheng and Liaozhong were clustered into one group and the other two populations, both collected from Songpu, were grouped together. There were obvious relations between genetic distances and geographical distributions of the five populations. No fragments were amplified from some loci of EST-SSRs, which may suggest the loss of these loci in mirror carp genome or sequence divergence at the primer binding sites. These null alleles may result from selection because functional genes are under more selection pressure than non-encoding loci. Overall, population genetic variation is high for each of the five mirror carp, and the differentiations are also significant among populations.

Alleles↗
PubMed2002

Evaluation of the performance of polished mirror surfaces for the TAMA gravitational wave detector by use of a wave-front tracing simulation.

We evaluated the performance of polished mirror surfaces for the TAMA interferometric gravitational wave detector by comparing the experimental results with a wave-front tracing simulation. The TAMA mirror surfaces were polished to a roughness of a few nanometer rms. We confirmed that these polished mirrors do not limit the present TAMA sensitivity and that the target shot-noise sensitivity will be achieved with these mirrors, even if a power-recycling technique is introduced in the next stage of the TAMA.

Journal Article↗
PubMed2003

Demonstration of a linear optical true-time delay device by use of a microelectromechanical mirror array.

We present the design and proof-of-concept demonstration of an optical device capable of producing true-time delay(s) (TTD)(s) for phased array antennas. This TTD device uses a free-space approach consisting of a single microelectromechanical systems (MEMS) mirror array in a multiple reflection spherical mirror configuration based on the White cell. Divergence is avoided by periodic refocusing by the mirrors. By using the MEMS mirror to switch between paths of different lengths, time delays are generated. Six different delays in 1-ns increments were demonstrated by using the Texas Instruments Digital Micromirror Device as the switching element. Losses of 1.6 to 5.2 dB per bounce and crosstalk of -27 dB were also measured, both resulting primarily from diffraction from holes in each pixel and the inter-pixel gaps of the MEMS.

Journal Article↗
PubMed2003

Design considerations for a highly segmented mirror.

Design issues for a 30-m highly segmented mirror are explored, with emphasis on parametric models of simple, inexpensive segments. A mirror with many small segments offers cost savings through quantity production and permits high-order active and adaptive wave-front corrections. For a 30-m f/1.5 paraboloidal mirror made of spherical, hexagonal glass segments, with simple warping harnesses and three-point supports, the maximum segment diameter is approximately 100 mm, and the minimum segment thickness is approximately 5 mm. Large-amplitude, low-order gravitational deformations in the mirror cell can be compensated if the segments are mounted on a plate floating on astatic supports. Because gravitational deformations in the plate are small, the segment actuators require a stroke of only a few tens of micrometers, and the segment positions can be measured by a wave-front sensor.

Journal Article↗
PubMed2003

Mirrors with regular hexagonal segments.

The point-spread function and emissivity are calculated for a mirror made from regular hexagonal segments of just a few different sizes. A mirror of this type has many similar segments, which is an advantage for manufacturing, and for an approximately f/1 mirror with > or = 1000 segments and > or = 4 sizes of regular hexagons the increase in intersegment gap area is negligible. This result raises the possibility of making a mirror from very large numbers of identical small segments that are warped to the required figure.

Journal Article↗
PubMed2004

Efficiency of an elliptically shaped x-ray mirror.

Curved reflecting mirrors are widely used as x-ray optical elements for both laboratory and synchrotron radiation sources. In general, the mirror parameters are optimized by numerical simulation. We discuss an analytical approach that is useful for deriving the mirror parameters, including eccentricity, length, angular acceptance, and magnification. We have examined in particular an elliptical surface from which we learned that, given the distance between the foci of the ellipse, the magnification, and the critical angle of total external reflection, it is possible to find analytically the optimal eccentricity that maximizes the angular acceptance and the optimal mirror length. We found that the last-named parameter, in a first approximation, depends only on the distance between the foci of the ellipse and on the magnification factor. We present as well a comparison of optimal parameters obtained with analytical calculation and with ray-tracing simulation that yielded good agreement.

Journal Article↗
PubMed2005

Methods for the characterization of deformable membrane mirrors.

We demonstrate two methods for the characterization of deformable membrane mirrors and the training of adaptive optics systems that employ these mirrors. Neither method employs a wave-front sensor. In one case, aberrations produced by a wave-front generator are corrected by the deformable mirror by use of a rapidly converging iterative algorithm based on orthogonal deformation modes of the mirror. In the other case, a simple interferometer is used with fringe analysis and phase-unwrapping algorithms. We discuss how the choice of singular values can be used to control the pseudoinversion of the control matrix.

Journal Article↗
PubMed2005

Multilayer silicon cavity mirrors for the far-infrared p-Ge laser.

Multilayer mirrors capable of > 99.9% reflectivity in the far infrared (70-200 microm wavelengths) were constructed using thin silicon etalons separated by empty gaps. Calculations indicate that only three periods are required to produce 99.9% reflectivity because of the large difference between the index of refraction of silicon (3.384) and the vacuum (1). The mirror was assembled from high-purity silicon wafers, with resistivity over 4000 omega cm to reduce free-carrier absorption. Wafers were double-side polished with faces parallel within 10 arc sec. The multilayer mirror was demonstrated as a cavity mirror for the far-infrared p-Ge laser. Dependence of reflectivity on design accuracy was considered.

Journal Article↗
PubMed2006

Interface engineered ultrashort period Cr-Ti multilayers as high reflectance mirrors and polarizers for soft x rays of lambda = 2.74 nm wavelength.

Cr-Ti multilayers with ultrashort periods of 1.39-2.04 nm have been grown for the first time as highly reflective, soft-x-ray multilayer, near-normal incidence mirrors for transition radiation and Cherenkov radiation x-ray sources based on the Ti-2p absorption edge at E = 452 eV (lambda = 2.74 nm). Hard, as well as soft, x-ay reflectivity and transmission electron microscopy were used to characterize the nanostructure of the mirrors. To achieve minimal accumulated roughness, improved interface flatness, and to avoid intermixing at the interfaces, each individual layer was engineered by use of a two-stage ion assistance process during magnetron sputter deposition: The first 0.3 nm of each Ti and Cr layer was grown without ion assistance, and the remaining 0.39-0.72 nm of the layers were grown with high ion-neutral flux ratios phi (phiTi = 3.3, phiCr = 2.2) and a low energy Eion (ETi = 23.7 and ECr = 21.2), ion assistance. A maximum soft-x-ray reflectivity of R = 2.1% at near-normal incidence (approximately 78.8 degrees) was achieved for a multilayer mirror containing 100 bilayers with a modulation period of 1.379 nm and a layer thickness ratio of tau = 0.5. For a polarizing multilayer mirror with 150 bilayers designed for operation at the Brewster angle, 45 degrees, an extinction ratio, Rs/Rp, of 266 was achieved with an absolute reflectivity of R = 4.3%.

Journal Article↗
PubMed2006

Gaussian-reflectivity mirror resonator for a high-power transverse-flow CO2 laser.

A Gaussian-reflectivity mirror resonator is proposed to achieve high-quality laser beams. To analyze the laser fields in a Gaussian-reflectivity mirror resonator, the diffraction integral equations of a Gaussian-reflectivity mirror resonator are converted to the finite-sum matrix equations. Consequently, according to the Fox-Li laser self-reproducing principle, we describe the mode fields and their losses in the proposed resonator as eigenvectors and eigenvalues of a transfer matrix. The conclusion can be drawn from the numerical results that, if a Gaussian-reflectivity mirror is adopted for a plano-concave resonator, a fundamental mode can easily be obtained from a transverse-flow CO2 laser and high-quality laser beams can be expected.

Journal Article↗
PubMed2006

Application of eigenmode in the adaptive optics system based on a micromachined membrane deformable mirror.

The construction process and characteristics of a deformable mirror eigenmode are introduced. The eigenmode of a 37-element micromachined membrane deformable mirror (MMDM) from OKO, Ltd. is analyzed. The Gaussian-Seidel low-order aberrations are fitted with eigenmodes as basic functions. An experimental adaptive optics (AO) system is constructed with the MMDM as the wavefront corrector, a deformable mirror eigenmode as the wavefront control algorithm, and a Shack-Hartmann wavefront sensor as the wavefront detector. The experimental results demonstrate that the deformable mirror eigenmode can act as the wavefront control algorithm for the AO system based on the MMDM.

Journal Article↗
PubMed2006

Storage ring free-electron lasing at 176 nm--dielectric mirror development for vacuum ultraviolet free-electron lasers.

Mirrors for storage ring free-electron lasers in the vacuum ultraviolet must provide adequate reflectivity and resistance against synchrotron radiation. The free-electron laser system at ELETTRA (Trieste, Italy) is targeted to lase in the spectral range between 155 and 200 nm. It was demonstrated that dense oxide multilayer coatings allow lasing down to 189.9 nm. However, pure oxide systems show significant absorption at lower wavelengths and cannot be employed below 189.9 nm. Fluoride stacks can be deposited down to 130 nm with high reflection values above 95%, but their resistance against the harsh synchrotron environment is poor. They rapidly degrade; lasing cannot be realized with this mirror approach. For the range between 170 and 190 nm, hybrid systems--combining fluoride and oxide materials--have been manufactured. With appropriate deposition procedures, mirrors achieve reflectance values up to 99% and an adequate radiation resistance simultaneously. A mirror based on a conventional fluoride stack protected by a dense silicon dioxide protection layer was deposited and successfully employed for free-electron lasing at 176.4 nm.

Journal Article↗
PubMed2006

Quasi-null lens optical system for the fabrication of an oblate convex ellipsoidal mirror: application to the Wide Angle Camera of the Rosetta space mission.

The design of a quasi-null lens system for the fabrication of an aspheric oblate convex ellipsoidal mirror is presented. The Performance and tolerance of the system have been analyzed. The system has been applied successfully for the fabrication of the primary mirror of the Wide Angle Camera (WAC), the imaging system onboard the Rosetta, the European Space Agency cornerstone mission dedicated to the exploration of a comet. The WAC is based on an off-axis two-mirror configuration, in which the primary mirror is an oblate convex ellipsoid with a significant conic constant.

Journal Article↗
PubMed2006

Simple yet accurate noncontact device for measuring the radius of curvature of a spherical mirror.

An easily reproducible device is demonstrated to be capable of measuring the radii of curvature of spherical mirrors, both convex and concave, without resorting to high-end interferometric or tactile devices. The former are too elaborate for our purposes, and the latter cannot be used due to the delicate nature of the coatings applied to mirrors used in high-power CO(2) laser applications. The proposed apparatus is accurate enough to be useful to anyone using curved optics and needing a quick way to assess the values of the radii of curvature, be it for entrance quality control or trouble shooting an apparently malfunctioning optical system. Specifically, the apparatus was designed for checking 50 mm diameter resonator (typically flat or tens of meters concave) and telescope (typically some meters convex and concave) mirrors for a high-power CO(2) laser, but it can easily be adapted to any other type of spherical mirror by a straightforward resizing.

Journal Article↗
PubMed2000

Wave-front sensing and deformable-mirror control in strong scintillation

Recent studies of coherent wave propagation through turbulence have shown that under conditions where scintillation is significant a continuous phase function does not in general exist, owing to the presence of branch points in the complex optical field. Because of branch points and the associated branch cuts, least-squares approaches to wave-front reconstruction and deformable-mirror control can have large errors. Branch-point reconstructors are known to provide superior performance to least-squares reconstructors, but they require that branch points be explicitly detected. Detecting branch points is a significant practical impediment owing to spatial sampling and measurement noise in real wave-front sensors. Branch points are associated with real zeros in an optical field, and hence information about the phase of the field is encoded in the amplitude of the wave. We present a new wave-front-sensor processing algorithm that exploits this observation in the wave-front-reconstruction and deformable-mirror-control process. This algorithm jointly processes three intensity measurements by using light from the beacon field to develop a set of deformable-mirror actuator commands that are maximally consistent with three intensity measurements: (1) the entire wave-front-sensor image, (2) a pupil intensity image, and (3) a conventional image. Owing to the nonlinear nature of the resulting algorithm, we have used a simulation to evaluate performance. We find that in a focused laser beam projection paradigm that uses a point-source beacon, the new algorithm provides significantly improved performance over that of conventional Hartmann sensor least-squares deformable-mirror control based on centroid processing of wave-front-sensor outputs. The performance of the new algorithm approaches, the performance of an idealized branch-point reconstructor that requires pointwise phase differences for operation.

Journal Article↗