Strip Geometry Research Articles

Confinement quantization of parallel pump instability threshold in a metallic ferromagnetic stripe

Lateral quantization of an excitation in a confined geometry is shown to lead to multiple cutoff thresholds for parametric processes. This idea is illustrated with a calculation of parallel pump instability thresholds for a ferromagnetic metallic stripe. The lateral quantization by the strip geometry results in thresholds which change discontinuously with increasing stripe width. Magnetostatic interactions create a secondary fine structure of kinks on the threshold curve. This effect should be possible to detect experimentally and be used for precise measurement of microwave losses in patterned magnetic metals.

Modelling orthogonal strip HPGe detector systems

The development of orthogonal planar strip high purity germanium (HPGe) detectors offers the advantages of good energy and three dimensional spatial resolution of photon interactions. The use of such devices for Positron emission Tomography (PET) are being investigated by the SmartPET collaboration. This paper presents initial results for algorithms developed to analyse the detector signals which recover the interaction position and energy, and the effects of strip geometry on these quantities. The aim is to develop a tool to aid design decisions, provide estimates of uncertainty, and resolve event position to better than 1 mm.

Properties of the multicritical point of±JIsing spin glasses on the square lattice

We use numerical transfer-matrix methods to investigate properties of the multicritical point of binary Ising spin glasses on a square lattice, whose location we assume to be given exactly by a conjecture advanced by Nishimori and Nemoto. We calculate the two largest Lyapunov exponents, as well as linear and nonlinear zero-field uniform susceptibilities, on strip of widths $4\ensuremath{\leqslant}L\ensuremath{\leqslant}16$ sites, from which we estimate the conformal anomaly $c$, the decay-of-correlations exponent $\ensuremath{\eta}$, and the linear and nonlinear susceptibility exponents $\ensuremath{\gamma}∕\ensuremath{\nu}$ and ${\ensuremath{\gamma}}^{\mathrm{nl}}∕\ensuremath{\nu}$, with the help of finite-size scaling and conformal invariance concepts. Our results are $c=0.46(1)$; $0.187\ensuremath{\lesssim}\ensuremath{\eta}\ensuremath{\lesssim}0.196$; $\ensuremath{\gamma}∕\ensuremath{\nu}=1.797(5)$; ${\ensuremath{\gamma}}^{\mathrm{nl}}∕\ensuremath{\nu}=5.59(2)$. A direct evaluation of correlation functions on the strip geometry, and of the statistics of the zeroth moment of the associated probability distribution, gives $\ensuremath{\eta}=0.194(1)$, consistent with the calculation via Lyapunov exponents. Overall, these values tend to be inconsistent with the universality class of percolation, though by small amounts. The scaling relation ${\ensuremath{\gamma}}^{\mathrm{nl}}∕\ensuremath{\nu}=2\ensuremath{\gamma}∕\ensuremath{\nu}+d$ (with space dimensionality $d=2$) is obeyed to rather good accuracy, thus showing no evidence of multiscaling behavior of the susceptibilities.

Dissipative Viscoplastic Deformation in Dynamic Fracture: Tip Blunting and Velocity Selection

Dynamic fracture in a wide class of materials reveals a "fracture energy" Gamma much larger than the expected nominal surface energy due to the formation of two fresh surfaces. Moreover, the fracture energy depends on the crack velocity, Gamma=Gamma(upsilon). We show that a simple dynamical theory of viscoplasticity coupled to asymptotic pure linear elasticity provides a possible explanation to the above phenomena. The theory predicts tip blunting characterized by a dynamically determined crack tip radius of curvature. In addition, we demonstrate velocity selection for cracks in fixed-grip strip geometry accompanied by the identification of Gamma and its velocity dependence.

Logarithmic corrections to correlation decay in two-dimensional random-bond Ising systems

The statistics of critical spin-spin correlation functions in Ising systems with nonfrustrated disorder are investigated on a strip geometry, via numerical transfer-matrix techniques. Conformal invariance concepts are used, in order to test for logarithmic corrections to pure power-law decay against distance. Fits of our data to conformal-invariance expressions, specific to logarithmic corrections to correlations on strips, give results with the correct sign, for the moments of order n = 0-4 of the correlation-function distribution. We find an interval of disorder strength along which corrections to pure-system behavior can be decomposed into the product of a known n -dependent factor and an approximately n -independent one, in accordance with predictions. A phenomenological fitting procedure is proposed, which takes partial account of subdominant terms of correlation-function decay on strips. In the low-disorder limit, it gives results in fairly good agreement with theoretical predictions, provided that an additional assumption is made.

Geometry and Elasticity of Strips and Flowers

We solve several problems that involve imposing metrics on surfaces. The problem of a strip with a linear metric gradient is formulated in terms of a Lagrangian similar to those used for spin systems. We are able to show that the low energy state of long strips is a twisted helical state like a telephone cord. We then extend the techniques used in this solution to two–dimensional sheets with more general metrics. We find evolution equations and show that when they are not singular, a surface is determined by knowledge of its metric, and the shape of the surface along one line. Finally, we provide numerical evidence by minimizing a suitable energy functional that once these evolution equations become singular, either the surface is not differentiable, or else the metric deviates from the target metric.

The LHCb silicon tracker

LHCb is a dedicated B-physics and CP-violation experiment for the Large Hadron Collider at CERN. Efficient track reconstruction and excellent trigger performances are essential in order to exploit fully its physics potential. Silicon strip detectors providing fast signal generation, high resolution and fine granularity are used for this purpose in the large area Trigger Tracker station in front of the spectrometer magnet and the LHCb Inner Tracker covering the area close to the beam pipe behind the magnet. Long read-out strips of up to 38 cm are used together with fast signal shaping adapted to the 25 ns LHC bunch crossing. The design of these tracking stations, the silicon sensor strip geometries and the latest test results are presented here.

Semiclassical energy levels of sine-Gordon model on a strip with Dirichlet boundary conditions

We derive analytic expressions of the semiclassical energy levels of sine-Gordon model in a strip geometry with Dirichlet boundary condition at both edges. They are obtained by initially selecting the classical backgrounds relative to the vacuum or to the kink sectors, and then solving the Schrödinger equations (of Lamè type) associated to the stability condition. Explicit formulas are presented for the classical solutions of both the vacuum and kink states and for the energy levels at arbitrary values of the size of the system. Their ultraviolet and infrared limits are also discussed.

Comparison between strip and rib SOI microwaveguides for intra-chip light distribution

A comparative analysis of the strip and rib geometries guided wave devices (waveguides, bends, mirrors, beam splitters) is performed to realize an optical distribution to several outputs. For the strip structures, the optical losses are strongly sensitive to sidewall roughness due to processing, whereas for slightly etched submicron rib waveguides, optical losses are lower than 0.4 dB/cm. The design, realization and characterization of an H-tree optical distribution from one input to 16 output points using 1 cm long rib waveguides, four compact T-splitters and two mirrors are presented. A 2.6lW optical power is obtained at each output for a 3 mW input power. This corresponds to an excess loss of 14 dB which seems to be sufficient for an integrated photodetector. � 2004 Elsevier B.V. All rights reserved.

Large-area Si(Li) orthogonal-strip detectors

Segmented lithium drifted silicon detectors are being developed for use in large Compton cameras and for medical imaging. We have successfully fabricated 3.5 mm thick crossed-strip detectors with active areas of 40/spl times/40 mm/sup 2/ with a 2 mm strip pitch. These detectors utilize new contact technology consisting of a boron implanted p-type contact and an amorphous silicon (/spl alpha/-Si) n-type contact. Good energy resolution and excellent strip separation was obtained from both contacts at relatively high operating temperatures. An energy resolution of 2.1 keV FWHM at 122 keV was obtained for the /spl alpha/-Si strip at temperatures up to 200 K and for the boron strip at temperatures up to 240 K. Measurements of the charge sharing between the strips were also performed. When the detector was flood illuminated with 60 keV gamma-rays, a small signal deficit was observed for events in which the signal was shared between two adjacent strips. The amount of deficit depended on the contact type, strip geometry and the operating temperature.

Modelling of diamond detectors: effects of the polycrystalline structure and a pulse shape analysis

Diamond is radiation-hard. This makes CVD diamond films suitable for particle detector applications without a significant degradation in performance due to radiation damage. We have built up a computer simulation of the detection mechanism in diamond detectors. We consider three different morphologies for the CVD diamond films: single crystal (SC), highly oriented (HOD), and randomly oriented polycrystalline (PCD) diamond. Our model of a diamond detector enables us to relate the morphology of the material and the geometry of the system to predict the detector's response. In this paper, we consider two different electrode configurations: parallel plate and interdigitated strips geometry; by applying the Shockley–Ramo theorem we calculate the total induced charge on the electrodes and we analyse some effects related to the presence of defects and other inhomogeneities related to the polycrystalline structure. In particular, we study the non-uniformity of the detector's response and the appearance of slow components in the output signal.

Optical wireless multibeam transmitter with line strip, diamond, and uniform geometries

We propose and evaluate a novel configuration that employs a multibeam transmitter in an optical wireless system. Such a configuration borrows attractive features from diffuse and line-of-sight systems, resulting in great robustness and ease of use. A line strip multibeam transmitter placed on the communication floor is proposed to produce a line of diffusing spots on the middle of the ceiling. The results associated with the new structure show that a receiver SNR improvement of about 3.8 dB can be achieved compared to the conventional diffuse configuration. Other geometries including a diamond-shaped spot geometry and a uniform spot geometry are also considered. Power distribution, received pulse shapes, and a comparison with the conventional diffuse link are outlined. SNR results show that the proposed geometries are very attractive.

Characterisation of an inhomogeneously irradiated microstrip detector using a fine spot infrared laser

A prototype silicon microstrip detector with p-strip read-out on oxygen enriched n-type substrate has been non-homogeneously irradiated using a 24 GeV/ c proton beam at the CERN-PS accelerator. The detector has a semicircular shape with radial strip geometry. The peak fluence received by the detector was 4.6×10 14 p/cm 2 though the non-uniform nature of the exposure left part of the detector unirradiated. The inhomogeneous irradiation introduced a damage profile in the detector approximating to that expected in the inner LHC region. High-irradiation gradients are important to study as they can modify the electric field within the silicon. Of special interest are changes in the component of the electric field parallel to the strip plane but perpendicular to the strips, which could lead to systematic shifts in the reconstructed cluster position. If these (flux and position dependent) shifts are sufficiently large they could contribute to degrading the spatial resolution of the detector. In order to quantify these effects, a precision narrow focus light spot from an infrared laser was used to investigate the charge collection properties of the sensor. Particular attention was devoted to the regions where a high gradient of the fluence will have introduced a large gradient in the effective local space charge. The results reported below place limits on the ‘distortions’ due to non-uniform irradiation.

Charge collection and charge sharing in heavily irradiated n-side read-out silicon microstrip detectors

Hadron radiation damage of n-bulk silicon detectors leads to a change in the effective space charge from positive to negative. This effect is called type inversion. Type inversion occurs after exposure to a fluence of a few 10 13 proton cm −2 and is characterized by migration of the diode junction to the n + implanted side (n-side) of the detector. After inversion the charge collection efficiency (CCE) of segmented detectors at low voltage is higher when the n-side, rather than the p-side, is read out. A p-side read out (p–in–n) and an n-side read out (n–in–n) strip detector with identical strip geometry and a wafer thickness of 200 μm were simultaneously and inhomogenously irradiated to a maximum fluence of 7×10 14 proton cm −2 with 24 GeV c −1 protons. A comparison of the CCE at very high irradiation doses is shown with these two read out geometries. The inhomogeneous irradiation induces an inhomogenous distribution of the effective space charge with a transverse component of the electric field that could in principle affect the resolution properties of the microstrip detector. The inter-strip charge sharing properties, as a function of dose, for the n–in–n detector have been measured. No systematic distortion of the reconstructed cluster position was detected within the limits of the measurement accuracy. The detectors were manufactured using oxygen enriched silicon substrates to limit the degradation of the full depletion voltage under charged hadron irradiation. The measured CCE confirms that the use of oxygenated n–in–n detectors is viable up to fluences of 7×10 14 proton cm −2.

Magnetic properties of arrays of superconducting strips in a perpendicular field

Current profiles and field lines and magnetization and ac losses are calculated for arrays of infinitely long superconducting strips in the critical state in a perpendicularly applied magnetic field. The strips are arranged vertically, horizontally, and in a matrix configuration, which are the geometries found in many actual high-${T}_{c}$ superconducting tapes. The finite thickness of the strips and the effects of demagnetizing fields are considered. Systematic results for the magnetization and ac losses of the arrays are obtained as function of the geometry and separation of the constituent strips. Results allow us to understand some unexplained features observed in experiments, as well as to propose some future directions.

Unequally spaced non‐periodic B‐spline finite strip method

AbstractThe unequally spaced non‐periodic B‐spline finite strip method (FSM) is presented. The motivation to investigate the irregularly spaced interior nodes in the longitudinal direction of strip is to generalize the concept of non‐periodic B‐spline FSM and to improve the general accuracy of the stress evaluation in the region of high stress gradients. In the present paper, the unequally spaced non‐periodic B3‐spline series with multiple knots at the boundary are introduced for the interpolation of displacement and description of geometry in the formulation of isoparametric spline FSM. The use of multiple knots at the boundary makes the shape function satisfy the Kronecker delta properties at the boundary. The unequally spaced B‐spline FSM is applied to the stress‐reduced shell problem with six degrees of freedom per node. The main purpose of this study is to find a way of ensuring that the geometry of strip is appropriately approximated when the interior nodes of the strip are not regularly spaced along the longitudinal direction. Some numerical results have been compared with those of the previous studies to evaluate the accuracy and efficiency of this method. Copyright © 2003 John Wiley & Sons, Ltd.

Modelling of diamond particle detectors: temperature dependence of the trapping and detrapping phenomena

We have built up a computer simulation of the detection mechanism for particles in diamond detectors. A detector with the interdigitated strip geometry is considered in this paper. Minimising ionising particles produce approximately 36 electron–hole pairs per micrometre along their path, which traverses the full thickness of the detector and alpha particles produce a large number of electron–hole pairs within a few micrometres of the surface. Under an applied electric field, the carriers move through the material and they induce charge on each electrode. By applying the Shockley–Ramo theorem we calculate this induced charge, which gives rise to the signal in an external circuit. In diamond, many of the carriers are trapped at defects in the material. They may recombine or be released at later times and continue their path contributing further to the signal. We have included these effects in the simulation and we have investigated the temperature dependence of the response of the detector.

On the dependence of dayside Kelvin-Helmholtz activity on IMF orientation

With its ≈12 h-long period of strongly northward magnetic field, the coronal mass ejection which passed Earth on April 11, 1997 afford an excellent opportunity of study Kelvin-Helmholtz (KH) activity at the dayside magnetopause as a function of the clock angle, θ, of the interplanetary field (IMF). A correlation between the wavelength of the KH waves and θ may be expected on the basis of our recent model, where activity is generated in strips which broaden as θ decreases. We identify two 2-hour long intervals of small, a preliminary test of model predictions, using records from two ground magnetometer chains, both on the dayside. Taking into account the local time of but different, clock angles, and make a preliminary test of model predictions, using records from two ground magnetometer chains, both on the dayside. Taking into accountthe local time of the magnetometer arrays and the geometry of the KH-active strips, we show that the resonant stations measured considerably more spectral power density in the 3–4 mHz range during the phase with smaller θ. Moreover, as θ increases, the spectral power spectrum shifted to higher frequencies that were almost absent for smaller θ.

Three-Dimensional Fracture Analysis and Experimental Investigation of Model Unidirectional Discontinuous Tow Composite Laminates

The purpose of this work is to perform analytical modeling and experimentally produce idealized composites reinforced with discontinuous fiber tows to evaluate the theoretical upper limits of tensile strength as compared to continuous fiber composites. The idealized composite represents a staggered mosaic of prepreg tape strips of equal width and length. Three-dimensional analysis was performed to evaluate the energy release rate of the possible damage accumulation modes, such as vertical splits and delaminations emanating from tape strip ends. Realistic estimates of the failure strain of the discontinued tow composites was obtained by comparing the calculated energy release rates to the critical Mode II energy release for axial cracking in the material system. The predicted failure strain as a function of the strip geometry was also in good correlation with the experimental results.

Closed-form solution for the size of plastic zone in an edge-cracked strip

This paper is concerned with the problem of plastic zone at the tip of an edge crack in an isotropic elastoplastic strip under anti-plane deformations. By means of complex potential and Dugdale model, the stress intensity factor and the size of plastic zone are obtained in closed-form. Furthermore, the analytic solutions for an edge crack at the free boundary of a half-space and a semi-infinite crack heading towards a free surface are determined as the limiting cases of the strip geometries.