11,013 research outputs found
Dynamic metasurface lens based on MEMS Technology
In the recent years, metasurfaces, being flat and lightweight, have been
designed to replace bulky optical components with various functions. We
demonstrate a monolithic Micro-Electro-Mechanical System (MEMS) integrated with
a metasurface-based flat lens that focuses light in the mid-infrared spectrum.
A two-dimensional scanning MEMS platform controls the angle of the lens along
the two orthogonal axes (tip-tilt) by +-9 degrees, thus enabling dynamic beam
steering. The device can compensate for off-axis incident light and thus
correct for aberrations such as coma. We show that for low angular
displacements, the integrated lens-on-MEMS system does not affect the
mechanical performance of the MEMS actuators and preserves the focused beam
profile as well as the measured full width at half maximum. We envision a new
class of flat optical devices with active control provided by the combination
of metasurfaces and MEMS for a wide range of applications, such as miniaturized
MEMS-based microscope systems, LIDAR scanners, and projection systems
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Diffusion Tensor Imaging for Assessment of Response to Neoadjuvant Chemotherapy in Patients With Breast Cancer.
In this study, the prognostic significance of tumor metrics derived from diffusion tensor imaging (DTI) was evaluated in patients with locally advanced breast cancer undergoing neoadjuvant therapy. DTI and contrast-enhanced magnetic resonance imaging were acquired at 1.5 T in 34 patients before treatment and after 3 cycles of taxane-based therapy (early treatment). Tumor fractional anisotropy (FA), principal eigenvalues (λ1, λ2, and λ3), and apparent diffusion coefficient (ADC) were estimated for tumor regions of interest drawn on DTI data. The association between DTI metrics and final tumor volume change was evaluated with Spearman rank correlation. DTI metrics were investigated as predictors of pathological complete response (pCR) by calculating the area under the receiver operating characteristic curve (AUC). Early changes in tumor FA and ADC significantly correlated with final tumor volume change post therapy (ρ = -0.38, P = .03 and ρ = -0.71, P < .001, respectively). Pretreatment tumor ADC was significantly lower in the pCR than in the non-pCR group (P = .04). At early treatment, patients with pCR had significantly higher percent changes of tumor λ1, λ2, λ3, and ADC than those without pCR. The AUCs for early percent changes in tumor FA and ADC were 0.60 and 0.83, respectively. The early percent changes in tumor eigenvalues and ADC were the strongest DTI-derived predictors of pCR. Although early percent change in tumor FA had a weak association with pCR, the significant correlation with final tumor volume change suggests that this metric changes with therapy and may merit further evaluation
Anchoring of semiotic symbols
This paper presents arguments for approaching the anchoring problem using {\em semiotic symbols}. Semiotic symbols are defined by a triadic relation between forms, meanings and referents, thus having an implicit relation to the real world.Anchors are formed between these three elements rather than between `traditional' symbols and sensory images. This allows an optimization between the form (i.e. the `traditional' symbol) and the referent. A robotic experiment based on adaptive language games illustrates how the anchoring of semiotic symbols can be achieved in a bottom-up fashion. The paper concludes that applying semiotic symbols is a potentially valuable approach toward anchoring
A "master" in base unpairing during isomerization of a promoter upon RNA polymerase binding
Isomerization of a closed to open complex of a promoter upon RNA polymerase binding involves base unpairing at the -10 region. After potassium permanganate sensitivity of unpaired thymine residues, we studied base unpairing at the -10 region during isomerization upon RNA polymerase binding at the P1 and P3 promoters of the gal operon. Substitution of adenine by 2-amino purine (2-AP) at the invariable A·T base pair at the -11 position of P1 and P3 prevented unpairing not only at that position but also at the other downstream positions, suggesting a "master" role of the adenine base at -11 of the template strand in overall base unpairing. 2-AP at -11 did not inhibit the formation of RNA polymerase·promoter complex and subsequent isomerization of the polymerase. Substitution of adenine by 2-AP at several other positions did not affect thymine unpairing. Changing the position of the amino group from C6 in adenine to C2 in 2-AP is mutational only at the master switch position, -11
Inelastic J/psi Photoproduction
Inelastic photoproduction of particles at high energies is one of
the processes to determine the gluon distribution in the nucleon. We have
calculated the QCD radiative corrections to the color-singlet model of this
reaction. They are large at moderate photon energies, but decrease with
increasing energies. The cross section and the energy spectrum are
compared with the available fixed-target photoproduction data and predictions
are given for the HERA energy range.Comment: 14 pages, latex, 7 uuencoded figure
AC Josephson effect in a gate-tunable CdAs nanowire superconducting weak link
Three-dimensional topological Dirac semimetals have recently gained
significant attention, since they possess exotic quantum states. When
constructing Josephson junctions utilizing these materials as the weak link,
the fractional ac Josephson effect emerges in the presence of a topological
supercurrent contribution. We investigate the ac Josephson effect in a Dirac
semimetal CdAs nanowire using two complementary methods: by probing the
radiation spectrum and by measuring Shapiro patterns. With both techniques, we
find that conventional supercurrent dominates at all investigated doping levels
and that any potentially present topological contribution falls below our
detection threshold. The inclusion of thermal noise in a resistively and
capacitively shunted junction (RCSJ) model allows us to reproduce the microwave
characteristics of the junction. With this refinement, we explain how weak
superconducting features can be masked and provide a framework to account for
elevated electronic temperatures present in realistic experimental scenarios
Color-Singlet and Color-Octet Contributions to Photoproduction
I discuss the impact of color-octet contributions and higher-order QCD
corrections on the cross section for inelastic photoproduction. The
theoretical predictions are compared with recent experimental data obtained at
HERA.Comment: LaTeX, 10 pages, 6 figures. Talk presented at the Workshops `QED and
QCD in Higher Orders', Rheinsberg, Germany, April 21-26 and `Quarkonium
Physics', Chicago, USA, June 13-15, 1996; to appear in the proceeding
Composition Dependence of Structural Parameters and Properties of Gallium Ferrite
We show the effect of composition on structural and magnetic characteristics
of pure phase polycrystalline GaFeO (GFO) for compositions between
0.8 <= x <= 1.3. X-ray analysis reveals that lattice parameters of GFO exhibit
a linear dependence on Fe content in single phase region indicating
manifestation of Vegard's law. Increasing Fe content of the samples also leads
to stretching of bonds as indicated by the Raman peak shifts. Further, low
temperature magnetic measurements show that the coercivity of the samples is
maximum for Ga:Fe ratio of 1:1 driven by a competition between decreasing
crystallite size and increasing magnetic anisotropy.Comment: 15 pages with 4 figure
Post microtextures accelerate cell proliferation and osteogenesis
AbstractThe influence of surface microtexture on osteogenesis was investigated in vitro by examining the proliferation and differentiation characteristics of a class of adult stem cells and their progeny, collectively known as connective tissue progenitor cells (CTPs). Human bone marrow-derived CTPs were cultured for up to 60days on smooth polydimethylsiloxane (PDMS) surfaces and on PDMS with post microtextures that were 10μm in diameter and 6μm in height, with 10μm separation. DNA quantification revealed that the numbers of CTPs initially attached to both substrates were similar. However, cells on microtextured PDMS transitioned from lag phase after 4days of culture, in contrast to 6days for cells on smooth surfaces. By day 9 cells on the smooth surfaces exhibited arbitrary flattened shapes and migrated without any preferred orientation. In contrast, cells on the microtextured PDMS grew along the array of posts in an orthogonal manner. By days 30 and 60 cells grew and covered all surfaces with extracellular matrix. Western blot analysis revealed that the expression of integrin α5 was greater on the microtextured PDMS compared with smooth surfaces. Real time reverse transcription-polymerase chain reaction revealed that gene expression of alkaline phosphatase had decreased by days 30 and 60, compared with that on day 9, for both substrates. Gene expression of collagen I and osteocalcin was consistently greater on post microtextures relative to smooth surfaces at all time points
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