75 FR 82070 - Light-Walled Rectangular Pipe and Tube From China, Korea, and Mexico
Federal Register 2010, 2011, 2012, 2013, 2014
2010-12-29
... permitted by section 201.8 of the Commission's rules, as amended, 67 FR 68036 (November 8, 2002). In... COMMISSION Light-Walled Rectangular Pipe and Tube From China, Korea, and Mexico AGENCY: United States...) Chapter 19 panel proceeding in Light-Walled Rectangular Pipe and Tube from Mexico, USA-MEX-1904-04,...
77 FR 3497 - Light-Walled Rectangular Pipe and Tube From Taiwan
Federal Register 2010, 2011, 2012, 2013, 2014
2012-01-24
... Procedure (19 CFR 207.2(f)). Background The Commission instituted this review on July 1, 2011 (76 FR 38691) and determined on October 4, 2011 that it would conduct an expedited review (76 FR 64105, October 17... COMMISSION Light-Walled Rectangular Pipe and Tube From Taiwan Determination On the basis of the record...
Federal Register 2010, 2011, 2012, 2013, 2014
2012-02-02
... Order; Light-Walled Welded Rectangular Carbon Steel Tubing From Taiwan, 54 FR 12467 (March 27, 1989). As... within a reasonably foreseeable time. See Light-Walled Rectangular Pipe and Tube From Taiwan, 77 FR 3497... of Five-Year (``Sunset'') Review, 76 FR 38613 (July 1, 2011) and Certain Pipe and Tube From...
Federal Register 2010, 2011, 2012, 2013, 2014
2012-01-27
... Administrative Reviews and Request for Revocation in Part, 76 FR 37781 (June 28, 2011) (Initiation Notice). This... International Trade Administration Light-Walled Rectangular Pipe and Tube From Turkey: Extension of Time Limits... administrative review for, inter alia, light- walled rectangular pipe and tube from Turkey for the May 1,...
Federal Register 2010, 2011, 2012, 2013, 2014
2013-07-16
... Commission found that the domestic interested party group responses to its notice of institution (78 FR 19526... COMMISSION Light-Walled Rectangular Pipe and Tube From China, Korea, Mexico, and Turkey: Notice of Commission... light-walled rectangular pipe and tube from China, Korea, Mexico, and Turkey would be likely to lead...
Federal Register 2010, 2011, 2012, 2013, 2014
2013-12-10
... COMMISSION Light-Walled Rectangular Pipe and Tube From China, Korea, Mexico, and Turkey; Scheduling of Full..., Mexico, and Turkey AGENCY: United States International Trade Commission. ACTION: Notice. SUMMARY: The... duty orders on light- walled rectangular pipe and tube from China, Korea, Mexico, and Turkey would...
Federal Register 2010, 2011, 2012, 2013, 2014
2011-09-07
...In response to requests for an administrative review, the Department of Commerce (the Department) is conducting an administrative review of the antidumping duty order on light-walled rectangular pipe and tube (LWR pipe and tube) from Mexico. The review covers imports of subject merchandise of two respondent companies during the period August 1, 2009, through July 31, 2010. For these......
Federal Register 2010, 2011, 2012, 2013, 2014
2013-08-06
... Determination of Sales at Less Than Fair Value, 73 FR 45403, 45405 (August 5, 2008); Notice of Antidumping Duty Order: Light-Walled Rectangular Pipe and Tube From Turkey, 73 FR 31065 (May 30, 2008). \\2\\ See Initiation of Five-Year (``Sunset'') Review, 78 FR 19647 (April 2, 2013) (Initiation). DATES: Effective...
Federal Register 2010, 2011, 2012, 2013, 2014
2010-01-13
... Duty Administrative Reviews and Requests for Revocation in Part, 74 FR 30052, August 25, 2009. The... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF COMMERCE International Trade Administration Light-Walled Rectangular Pipe and Tube from Turkey: Extension of Time...
Federal Register 2010, 2011, 2012, 2013, 2014
2011-01-25
... Antidumping and Countervailing Duty Administrative Reviews and Requests for Revocation in Part, 75 FR 37759... From the Federal Register Online via the Government Publishing Office DEPARTMENT OF COMMERCE International Trade Administration Light-Walled Rectangular Pipe and Tube From Turkey: Extension of Time...
Federal Register 2010, 2011, 2012, 2013, 2014
2013-04-01
... pipe and tube from Turkey (73 FR 31065). On August 5, 2008, the Department of Commerce issued a countervailing duty order on imports of light-walled rectangular pipe and tube from China (73 FR 45405) and... part 207), as most recently amended at 74 FR 2847 (January 16, 2009). \\1\\ No response to this...
Federal Register 2010, 2011, 2012, 2013, 2014
2011-10-18
...) of the Act. See Initiation of Five-Year (``Sunset'') Review, 76 FR 38613 (July 1, 2011) (Notice of... FR 12467 (March 27, 1989). The Department received a notice of intent to participate in this sunset... International Trade Administration Light-Walled Welded Rectangular Carbon Steel Tubing From Taiwan:...
Federal Register 2010, 2011, 2012, 2013, 2014
2011-06-08
...In response to a request from Noksel Celik Boru Sanayi A.S., (Noksel), the Department of Commerce (the Department) is conducting an administrative review of the antidumping duty order on light-walled rectangular pipe and tube from Turkey. Atlas Tube, Inc. and Searing Industries, Inc. are petitioners in this case. The review covers exports of the subject merchandise to the United States......
Federal Register 2010, 2011, 2012, 2013, 2014
2010-12-10
...; Opportunity To Request Administrative Review, 75 FR 45094 (August 2, 2010). On August 16, 2010, the Department... Duty Administrative Reviews and Requests for Revocation in Part, 75 FR 60076 (September 29, 2010...). The review covers Sun Group Co., Ltd. (Sun Group), a producer/exporter of light-walled...
Federal Register 2010, 2011, 2012, 2013, 2014
2010-05-14
... Rectangular Pipe and Tube from the People's Republic of China, 73 FR 35652 (June 24, 2008). On August 5, 2008... Determination of Sales at Less Than Fair Value, 73 FR 45403 (August 5, 2008). On August 3, 2009, the Department... Administrative Review, 74 FR 38397 (August 3, 2009). Based on a timely request from FitMAX for an...
Federal Register 2010, 2011, 2012, 2013, 2014
2010-10-04
... Tube from Turkey; Notice of Preliminary Results of Antidumping Duty Administrative Review, 75 FR 33779...-Walled Rectangular Pipe and Tube From Turkey, 73 FR 31065 (May 30, 2008). See Assessment of Antidumping... FR 23954 (May 6, 2003) (Assessment of Antidumping Duties). This clarification will apply to...
75 FR 32341 - Import Administration IA ACCESS Pilot Program
Federal Register 2010, 2011, 2012, 2013, 2014
2010-06-08
... from the People's Republic of China--Investigation; A-588-857: Welded Large Diameter Line Pipe from... program will implement IA ACCESS on a small scale to allow the Department to evaluate and gain experience... from Mexico-- Administrative Review 07/01/08-06/30/09; A-201-836: Light-Walled Rectangular Pipe...
Federal Register 2010, 2011, 2012, 2013, 2014
2013-03-01
...; Policy Bulletin, 63 FR 18871 (April 16, 1998). The Notice of Initiation of Five-Year (``Sunset'') Reviews... Tube from Dana Mermelstein, (202) 482-1391. Korea (A-580-859) (1st Review). Light-Walled Rectangular Pipe and Tube from Dana Mermelstein, (202) 482-1391. Mexico (A-201-836) (1st Review)....
Light walls around sunspots observed by the Interface Region Imaging Spectrograph
NASA Astrophysics Data System (ADS)
Hou, Y. J.; Li, T.; Yang, S. H.; Zhang, J.
2016-05-01
Context. The Interface Region Imaging Spectrograph (IRIS) mission provides high-resolution observations of the chromosphere and transition region. Using these data, some authors have reported the new finding of light walls above sunspot light bridges. Aims: We try to determine whether the light walls exist somewhere else in active regions in addition to the light bridges. We also examine how the material of these walls evolves. Methods: Employing six months of (from 2014 December to 2015 June) high tempo-spatial data from the IRIS, we find many light walls either around sunspots or above light bridges. Results: For the first time, we report one light wall near an umbral-penumbral boundary and another along a neutral line between two small sunspots. The former light wall has a multilayer structure and is associated with the emergence of positive magnetic flux in the ambient negative field. The latter light wall is associated with a filament activation, and the wall body consists of the filament material, which flowed to a remote plage region with a negative magnetic field after the light wall disappeared. Conclusions: These new observations reveal that these light walls are multilayer and multithermal structures that occur along magnetic neutral lines in active regions. Movies associated to Figs. 1-4 are available in electronic form at http://www.aanda.org
Light walls around sunspots observed by the Interface Region Imaging Spectrograph
NASA Astrophysics Data System (ADS)
Hou, Y. J.; Li, T.; Yang, S. H.; Zhang, J.
2016-04-01
Context. The Interface Region Imaging Spectrograph (IRIS) mission provides high-resolution observations of the chromosphere and transition region. Using these data, some authors have reported the new finding of light walls above sunspot light bridges. Aims: We try to determine whether the light walls exist somewhere else in active regions in addition to the light bridges. We also examine how the material of these walls evolves. Methods: Employing six months of (from 2014 December to 2015 June) high tempo-spatial data from the IRIS, we find many light walls either around sunspots or above light bridges. Results: For the first time, we report one light wall near an umbral-penumbral boundary and another along a neutral line between two small sunspots. The former light wall has a multilayer structure and is associated with the emergence of positive magnetic flux in the ambient negative field. The latter light wall is associated with a filament activation, and the wall body consists of the filament material, which flowed to a remote plage region with a negative magnetic field after the light wall disappeared. Conclusions: These new observations reveal that these light walls are multilayer and multithermal structures that occur along magnetic neutral lines in active regions. Movies associated to Figs. 1-4 are available in electronic form at http://www.aanda.org
Federal Register 2010, 2011, 2012, 2013, 2014
2012-09-10
... Administrative Review, 77 FR 33395 (June 6, 2012) (Preliminary Results). DATES: Effective September 10, 2012. FOR... of Antidumping Duties, 68 FR 23954 (May 6, 2003) (Assessment Policy Notice). Cash Deposit... Turkey, 73 FR 31065 (May 30, 2008). Notification to Importers This notice serves as a final reminder...
Federal Register 2010, 2011, 2012, 2013, 2014
2013-01-08
... Mexico: Preliminary Results and Partial Rescission of Antidumping Duty Administrative Review, 77 FR 55186... Than Fair Value, 73 FR 45403, 45405 (August 5, 2008). In accordance with 19 CFR 356.8(a), the... percent of copper, or 0.50 percent of aluminum, or 1.25 percent of chromium, or 0.30 percent of cobalt,...
Federal Register 2010, 2011, 2012, 2013, 2014
2012-01-12
... Rescission of Antidumping Duty Administrative Review, 76 FR 55352 (September 7, 2011) (Preliminary Results... review for two other companies. See Preliminary Results, 76 FR at 55353. \\2\\ See Initiation of Antidumping and Countervailing Duty Administrative Reviews and Requests for Revocation in Part, 75 FR...
Federal Register 2010, 2011, 2012, 2013, 2014
2010-09-21
... Administrative Review, 75 FR 27308 (May 14, 2010) (``Preliminary Results''). We gave interested parties an... copper, or 0.50 percent of aluminum, or 1.25 percent of chromium, or 0.30 percent of cobalt, or...
Federal Register 2010, 2011, 2012, 2013, 2014
2011-01-06
... FR at 55567. Respondent companies Nacional de Acero S.A. de C.V., Regiomontana de Perfiles y Tubos S... Mexico: Preliminary Results of Antidumping Duty Administrative Review, 75 FR 55559 (September 13,...
Federal Register 2010, 2011, 2012, 2013, 2014
2013-09-06
... Republic of Korea: Notice of Amended Final Determination of Sales at Less Than Fair Value, 73 FR 45403...; Final Modification, 77 FR 8101 (February 14, 2012). The Department clarified its ``automatic assessment... Proceedings: Assessment of Antidumping Duties, 68 FR 23954 (May 6, 2003). In accordance with 19 CFR...
Federal Register 2010, 2011, 2012, 2013, 2014
2012-09-07
... From Mexico: Preliminary Results of Antidumping Duty Administrative Review, 75 FR 55559 (September 13... Mexico: Preliminary Results of Antidumping Duty Administrative Review, 75 FR 55559, 55565-55566... Suspended Investigation; Opportunity To Request Administrative Review, 76 FR 45773 (August 1, 2011). \\2\\...
Federal Register 2010, 2011, 2012, 2013, 2014
2011-02-18
... Administrative Review, 75 FR 55559 (September 13, 2010) (Preliminary Results). This first administrative review... Administrative Reviews and Request for Revocation in Part, 74 FR 48224, 48225 (September 22, 2009). We invited... Final Results of Antidumping Duty Administrative Review, 76 FR 774 (January 6, 2011). Period of...
Federal Register 2010, 2011, 2012, 2013, 2014
2011-10-17
... interested party group response to its notice of institution (76 FR 38691, July 1, 2011) of the subject five... Commission's rules. Please consult the Commission's rules, as amended, 76 FR 61937 (Oct. 6, 2011) and the Commission's Handbook on Filing Procedures, 76 FR 62092 (Oct. 6, 2011), available on the Commission's...
Federal Register 2010, 2011, 2012, 2013, 2014
2013-08-08
... People's Republic of China, 73 FR 45405 (August 5, 2008). On April 2, 2013, the Department initiated the... Act). See Initiation of Five-Year (``Sunset'') Review, 78 FR 19647 (April 2, 2013). The Department received a notice of intent to participate from the following domestic parties: Bull Moose Tube...
Federal Register 2010, 2011, 2012, 2013, 2014
2010-09-13
... Than Fair Value, 73 FR 45403 (August 5, 2008) (Order). On August 3, 2009, the Department published in... Request Administrative Review, 74 FR 38397 (August 3, 2009), covering, inter alia, LWRPT from Mexico for... for Revocation in Part, 74 FR 48224 (September 22, 2009) (Initiation Notice).\\3\\ \\3\\ As noted in...
Federal Register 2010, 2011, 2012, 2013, 2014
2011-09-19
... Tube From Turkey; Notice of Preliminary Results of Antidumping Duty Administrative Review, 76 FR 33200... From Turkey, 73 FR 31065 (May 30, 2008). See Assessment of Antidumping Duties for a full discussion of... filing case briefs. See Preliminary Results, 76 FR at 33204. No interested party submitted briefs....
Federal Register 2010, 2011, 2012, 2013, 2014
2012-06-06
... Order, Finding, or Suspended Investigation; Opportunity To Request Administrative Review, 76 FR 24460... Industries, Inc., are petitioners in this case. The review covers exports of the subject merchandise to the... Reviews and Request for Revocation in Part, 76 FR 37781 (June 28, 2011). On August 5, 2011, the...
Federal Register 2010, 2011, 2012, 2013, 2014
2010-06-15
... Quality Steel Products from Brazil; Preliminary Results of Antidumping Duty Administrative Review, 70 FR...: Carbon and Certain Alloy Steel Wire Rod from Canada, 71 FR 3822 (January 24, 2006), and accompanying...'') or CV during the same shorter averaging periods. See Stainless Steel Plate in Coils From...
Federal Register 2010, 2011, 2012, 2013, 2014
2010-11-09
... Administrative Review, 75 FR 45094 (August 2, 2010). On August 30, 2010, in accordance with 19 CFR 351.213(b), the Department received a timely request from Sun Group Co., Ltd. (``Sun Group'') to conduct an... Requests for Revocation in Part, 75 FR 60076, 60082 (September 29, 2010). Rescission of Countervailing...
Transport in rectangular quadrupole channels
Meier, E.
1983-08-01
Multiple electrostatic quadrupole arrays can be produced in many different geometries. However, the fabrication process can be considerably simplified if the poles are rectangular. This is especially true for millimeter sized channels. This paper presents the results of a series of measurements comparing the space charge limits in cylindrical and rectangular quadrupole channels.
Phasing rectangular apertures.
Baker, K L; Homoelle, D; Utterback, E; Jones, S M
2009-10-26
Several techniques have been developed to phase apertures in the context of astronomical telescopes with segmented mirrors. Phasing multiple apertures, however, is important in a wide range of optical applications. The application of primary interest in this paper is the phasing of multiple short pulse laser beams for fast ignition fusion experiments. In this paper analytic expressions are derived for parameters such as the far-field distribution, a line-integrated form of the far-field distribution that could be fit to measured data, enclosed energy or energy-in-a-bucket and center-of-mass that can then be used to phase two rectangular apertures. Experimental data is taken with a MEMS device to simulate the two apertures and comparisons are made between the analytic parameters and those derived from the measurements. Two methods, fitting the measured far-field distribution to the theoretical distribution and measuring the ensquared energy in the far-field, produced overall phase variance between the 100 measurements of less than 0.005 rad(2) or an RMS displacement of less than 12 nm. PMID:19997175
Analysis of rectangular microstrip antennas
NASA Technical Reports Server (NTRS)
Bailey, M. C.; Deshpande, M. D.
1984-01-01
The problem of microstrip antennas covered by a dielectric substrate is formulated in terms of coupled integro-differential equations with the current distribution on the conducting patch as an unknown quantity. The Galerkin method is used to solve for the unknown patch current. Using the present formulation, the radiation pattern, the resonant frequency, and the bandwidth of a rectangular microstrip antenna are computed. Design data for a rectangular microstrip antenna are also presented.
Synchronizability of random rectangular graphs
Estrada, Ernesto Chen, Guanrong
2015-08-15
Random rectangular graphs (RRGs) represent a generalization of the random geometric graphs in which the nodes are embedded into hyperrectangles instead of on hypercubes. The synchronizability of RRG model is studied. Both upper and lower bounds of the eigenratio of the network Laplacian matrix are determined analytically. It is proven that as the rectangular network is more elongated, the network becomes harder to synchronize. The synchronization processing behavior of a RRG network of chaotic Lorenz system nodes is numerically investigated, showing complete consistence with the theoretical results.
Rectangular configuration improves superconducting cable
NASA Technical Reports Server (NTRS)
Foss, M.; Laverick, C.; Lobell, G.
1968-01-01
Superconducting cable for a cryogenic electromagnet with improved mechanical and thermal properties consists of a rectangular cross-sectioned combination of superconductor and normal conductor. The conductor cable has superconductors embedded in a metallic coating with high electrical and mechanical conductivity at liquid helium temperatures.
Rectangular groupoids and related structures
Boykett, Tim
2013-01-01
The quasivariety of groupoids (N,∗) satisfying the implication a∗b=c∗d⇒a∗d=c∗b=a∗b generalises rectangular semigroups and central groupoids. We call them rectangular groupoids and find three combinatorial structures based upon arrays, matrices and graphs that are closely related. These generalise several groupoids of independent interest. The quasivariety generates the variety of all groupoids; they satisfy no nontrivial equations. We see some strong connections with isotopy, this being one of the classes of algebras (along with quasigroups) closed under isotopy. We investigate some constructions and show that a regular automorphism exists iff the groupoid is derived from a group via a Cayley graph construction. PMID:23836949
Rectangular subsonic jet flowfield study
NASA Technical Reports Server (NTRS)
Morrison, Gerald L.; Tatterson, Gary B.; Swan, David H.
1987-01-01
The flowfield of a rectangular jet with 2:1 aspect ratio was studied at an axial Reynolds number of 127,000, using a three-dimensional laser anemometer. The flowfield surveys resulted in mean velocity vector field plots and contour plots of the Reynolds stress tensor components for the major and minor axes. These data contribute substantially to currently available data of jet flowfields.
Designing Rectangular RHCP Microstrip Antennas
NASA Technical Reports Server (NTRS)
Davidson, Shayla E.
1987-01-01
RHCP, Right-Handed, Circularly Polarized Microstrip Antenna program, aids in design of rectangular microstrip-antenna element, given desired frequency of operation and characteristics of substrate. Begins design calculations on basis of square element with linear polarization. Effective dielectric constant and changes in electrical length due to fringing at edges of radiating element taken into account. Coaxial feed inset with 50 ohms input impedance. Placement of feed such that two orthonormal modes produced in antenna cavity, right- or left-handed circular polarization obtained. Written in FORTRAN 77.
Mapping from rectangular to harmonic representation
Schneider, W.; Bateman, G.
1986-08-01
An algorithm is developed to determine the Fourier harmonics representing the level contours of a scalar function given on a rectangular grid. This method is applied to the problem of computing the flux coordinates and flux surface average needed for 1-1/2-D transport codes and MHD stability codes from an equilibrium flux function given on a rectangular grid.
ac electroosmosis in rectangular microchannels.
Campisi, Michele; Accoto, Dino; Dario, Paolo
2005-11-22
Motivated by the growing interest in ac electroosmosis as a reliable no moving parts strategy to control fluid motion in microfluidic devices for biomedical applications, such as lab-on-a-chip, we study transient and steady-state electrokinetic phenomena (electroosmosis and streaming currents) in infinitely extended rectangular charged microchannels. With the aid of Fourier series and Laplace transforms we provide a general formal solution of the problem, which is used to study the time-dependent response to sudden ac applied voltage differences in case of finite electric double layer. The Debye-Huckel approximation has been adopted to allow for an algebraic solution of the Poisson-Boltzmann problem in Fourier space. We obtain the expressions of flow velocity profiles, flow rates, streaming currents, as well as expressions of the complex hydraulic and electrokinetic conductances. We analyze in detail the dependence of the electrokinetic conductance on the extension of linear dimensions relative to the Debye length, with an eye on finite electric double layer effects. PMID:16351310
Partial Rectangular Metric Spaces and Fixed Point Theorems
2014-01-01
The purpose of this paper is to introduce the concept of partial rectangular metric spaces as a generalization of rectangular metric and partial metric spaces. Some properties of partial rectangular metric spaces and some fixed point results for quasitype contraction in partial rectangular metric spaces are proved. Some examples are given to illustrate the observed results. PMID:24672366
Turbulence Measurements of Rectangular Nozzles with Bevel
NASA Technical Reports Server (NTRS)
Bridges, James; Wernet, Mark P.
2015-01-01
This paper covers particle image velocimetry measurements of a family of rectangular nozzles with aspect ratios 2, 4, and 8, in the high subsonic flow regime. Far-field acoustic results, presented previously, showed that increasing aspect ratios increased the high frequency noise, especially directed in the polar plane containing the minor axis of the nozzle. The measurements presented here have important implications in the modeling of turbulent sources for acoustic analogy theories. While the nonaxisymmetric mean flow from the rectangular nozzles can be studied reliably using computational solutions, the nonaxisymmetry of the turbulent fluctuations, particularly at the level of velocity components, cannot; only measurements such as these can determine the impact of nozzle geometry on acoustic source anisotropy. Additional nozzles were constructed that extended the wide lip on one side of these nozzles to form beveled nozzles. The paper first documents the velocity fields, mean and variance, from the round, rectangular, and beveled rectangular nozzles at high subsonic speeds. A second section introduces measures of the isotropy of the turbulence, such as component ratios and lengthscales, first by showing them for a round jet and then for the rectangular nozzles. From these measures the source models of acoustic analogy codes can be judged or modified to account for these anisotropies.
Electrochemical apparatus comprising modified disposable rectangular cuvette
Dattelbaum, Andrew M; Gupta, Gautam; Morris, David E
2013-09-10
Electrochemical apparatus includes a disposable rectangular cuvette modified with at least one hole through a side and/or the bottom. Apparatus may include more than one cuvette, which in practice is a disposable rectangular glass or plastic cuvette modified by drilling the hole(s) through. The apparatus include two plates and some means of fastening one plate to the other. The apparatus may be interfaced with a fiber optic or microscope objective, and a spectrometer for spectroscopic studies. The apparatus are suitable for a variety of electrochemical experiments, including surface electrochemistry, bulk electrolysis, and flow cell experiments.
Comparing the Volumes of Rectangular Prisms
ERIC Educational Resources Information Center
Assuah, Charles K.; Wiest, Lynda R.
2010-01-01
Can middle-grades students determine which of two rectangular prisms has a larger volume? Can they do so without using a formula? Geometry, and particularly the concept of volume, is important in many subjects, such as physics and chemistry. Students greatly enhance their mathematics knowledge when they make generalizations and construct arguments…
Rectangular Microstrip Antenna with Slot Embedded Geometry
NASA Astrophysics Data System (ADS)
Ambresh, P. A.; Hadalgi, P. M.; Hunagund, P. V.; Sujata, A. A.
2014-09-01
In this paper, a novel design that improves the performance of conventional rectangular microstrip antenna is discussed. Design adopts basic techniques such as probe feeding technique with rectangular inverted patch structure as superstrate, air filled dielectric medium as substrate and slot embedded patch. Prototype of the proposed antenna has been fabricated and various antenna performance parameters such as impedance bandwidth, return loss, radiation pattern and antenna gain are considered for Electromagnetic-study. The antennas are designed for the wireless application operating in the frequency range of 3.3 GHz to 3.6 GHz, and UK based fixed satellite service application (3 GHz to 4 GHz), and are named as single inverted patch conventional rectangular microstrip antenna (SIP-CRMSA) and slots embedded inverted patch rectangular microstrip antenna (SEIP-RMSA), respectively. Measurement outcomes for SEIP-RMSA1 and SEIP-RMSA2 showed the satisfactory performance with an achievable impedance bandwidth of 260 MHz (7 %) and 250 MHz (6.72 %), with return loss (RL) of -11.06 dB and -17.98 dB, achieved gain of 8.17 dB and 5.17 dB with 10% and 8% size reduction in comparison with the conventional patch antenna.
Normal-Pressure Tests of Rectangular Plates
NASA Technical Reports Server (NTRS)
Ramberg, Walter; Mcpherson, Albert E; Levy, Samuel
1942-01-01
Report presents the results of normal-pressure tests made of 56 rectangular plates with clamped edges and of 5 plates with freely supported edges. Pressure was applied and the center deflection and the permanent set at the center were measured. For some of the plates, in addition, strains and contours were measured.
Eigenvalues of Rectangular Waveguide Using FEM With Hybrid Elements
NASA Technical Reports Server (NTRS)
Deshpande, Manohar D.; Hall, John M.
2002-01-01
A finite element analysis using hybrid triangular-rectangular elements is developed to estimate eigenvalues of a rectangular waveguide. Use of rectangular vector-edge finite elements in the vicinity of the PEC boundary and triangular elements in the interior region more accurately models the physical nature of the electromagnetic field, and consequently quicken the convergence.
RWGSCAT - RECTANGULAR WAVEGUIDE JUNCTION SCATTERING PROGRAM
NASA Technical Reports Server (NTRS)
Hoppe, D. J.
1994-01-01
In order to optimize frequency response and determine the tolerances required to meet RF specifications, accurate computer modeling of passive rectangular waveguide components is often required. Many rectangular waveguide components may be represented either exactly or approximately as a number of different size rectangular waveguides which are connected in series. RWGSCAT, Rectangular WaveGuide junction SCATtering program, solves for the scattering properties of a waveguide device. This device must consist of a number of rectangular waveguide sections of different cross sectional area which are connected in series. Devices which fall into this category include step transformers, filters, and smooth or corrugated rectangular horns. RWGSCAT will model such devices and accurately predict the reflection and transmission characteristics, taking into account higher order (other than dominant TE 10) mode excitation if it occurs, as well as multiple reflections and stored energy at each discontinuity. For devices which are large with respect to the wavelength of operation, the characteristics of the device may be required for computing a higher order mode or a number of higher order modes exciting the device. Such interactions can be represented by defining a scattering matrix for each discontinuity in the device, and then cascading the individual scattering matrices in order to determine the scattering matrix for the overall device. The individual matrices are obtained using the mode matching method. RWGSCAT is written in FORTRAN 77 for IBM PC series and compatible computers running MS-DOS. It has been successfully compiled and implemented using Lahey FORTRAN 77 under MS-DOS. A sample MS-DOS executable is provided on the distribution medium. It requires 377K of RAM for execution. Sample input data is also provided on the distribution medium. The standard distribution medium for this program is one 5.25 inch 360K MS-DOS format diskette. The contents of the diskette are
Film condensation in a horizontal rectangular duct
NASA Technical Reports Server (NTRS)
Lu, Qing; Suryanarayana, N. V.
1993-01-01
Condensation heat transfer in a horizontal rectangular duct was experimentally and analytically investigated. To prevent the dripping of condensate on the film, the experiment was conducted inside a horizontal rectangular duct with vapor condensing only on the bottom cooled plate of the duct. R-113 and FC-72 (Fluorinert Electronic Fluid developed by the 3M Company) were used as the condensing fluids. The experimental program included measurements of film thickness, local and average heat transfer coefficients, wave length, wave speed, and a study of wave initiation. The measured film thickness was used to obtain the local heat transfer coefficient. The wave initiation was studied both with condensation and with an adiabatic air-liquid flow. The test sections used in both experiments were identical.
Eddy viscosity measurements in a rectangular jet
NASA Technical Reports Server (NTRS)
Swan, David H.; Morrison, Gerald L.
1988-01-01
The flow field of a rectangular jet with a 2:1 aspect ratio was studied at a Reynolds number of 100,000 (Mach number 0.09) using three-dimensional laser Doppler velocimetry (LDV). Velocity gradients, Reynolds stress tensor components, and scalar eddy viscosities are presented for the major and minor axis planes of the jet. The eddy viscosity model was found to be applicable only in the direction of maximum mean velocity gradient.
Rectangular shape distributed piezoelectric actuator: analytical analysis
NASA Astrophysics Data System (ADS)
Sun, Bohua; Qiu, Yan
2004-04-01
This paper is focused on the development of distributed piezoelectric actuators (DPAs) with rectangular shapes by using PZT materials. Analytical models of rectangular shape DPAs have been constructed in order to analyse and test the performance of DPA products. Firstly, based on the theory of electromagnetics, DPAs have been considered as a type of capacitor. The charge distributed density on the interdigitated electrodes (IDEs), which has been applied in the actuators, and the capacitance of the DPAs have been calculated. The accurate distribution and intensity of electrical field in DPA element have also been calculated completely. Secondly, based on the piezoelectric constitutive relations and the compound plates theory, models for mechanical strain and stress fields of DPAs have been developed, and the performances of rectangular shape DPAs have been discussed. Finally, on the basis of the models that have been developed in this paper, an improved design of a rectangular shape DPA has been discussed and summed up. Due to the minimum hypotheses that have been used during the processes of calculation, the characteristics of this paper are that the accurate distribution and intensity of electrical fields in DPAs have been concluded. The proposed accurate calculations have not been seen in the literature, and can be used in DPA design and manufacture processes in order to improve mechanical performance and reduce the cost of DPA products in further applications. In this paper, all the processes of analysis and calculation have been done by MATLAB and MathCAD. The FEM results used for comparison were obtained using the ABAQUS program.
A clamped rectangular plate containing a crack
NASA Technical Reports Server (NTRS)
Tang, R.; Erdogan, F.
1985-01-01
The general problem of a rectangular plate clamped along two parallel sides and containing a crack parallel to the clamps is considered. The problem is formulated in terms of a system of singular integral equations and the asymptotic behavior of the stress state near the corners is investigated. Numerical examples are considered for a clamped plate without a crack and with a centrally located crack, and the stress intensity factors and the stresses along the clamps are calculated.
Efficient Algorithm for Rectangular Spiral Search
NASA Technical Reports Server (NTRS)
Brugarolas, Paul; Breckenridge, William
2008-01-01
An algorithm generates grid coordinates for a computationally efficient spiral search pattern covering an uncertain rectangular area spanned by a coordinate grid. The algorithm does not require that the grid be fixed; the algorithm can search indefinitely, expanding the grid and spiral, as needed, until the target of the search is found. The algorithm also does not require memory of coordinates of previous points on the spiral to generate the current point on the spiral.
Rectangular Pulsed Laser-Electromagnetic Hybrid Accelerator
Kishida, Yoshiaki; Katayama, Masahiro; Horisawa, Hideyuki
2010-10-13
Experimental investigation of impulse-bit and propellant consumption rate, or mass shot, per single pulse discharge was conducted to characterize the thrust performance of the rectangular laser-electromagnetic hybrid acceleration thruster with various propellant materials. From the result, alumina propellant showed significantly superior performance. The largest values of the measured impulse-bit, specific impulse and thrust efficiency were 49 {mu}Nsec, 6,200 sec and 22%, respectively.
Acoustic Measurements of Rectangular Nozzles With Bevel
NASA Technical Reports Server (NTRS)
Bridges, James E.
2012-01-01
A series of convergent rectangular nozzles of aspect ratios 2:1, 4:1, and 8:1 were constructed with uniform exit velocity profiles. Additional nozzles were constructed that extended the wide lip on one side of these nozzles to form beveled nozzles. Far-field acoustic measurements were made and analyzed, and the results presented. The impact of aspect ratio on jet noise was similar to that of enhanced mixing devices: reduction in aft, peak frequency noise with an increase in broadside, high frequency noise. Azimuthally, it was found that rectangular jets produced more noise directed away from their wide sides than from their narrow sides. The azimuthal dependence decreased at aft angles where noise decreased. The effect of temperature, keeping acoustic Mach number constant, was minimal. Since most installations would have the observer on the wide size of the nozzle, the increased high frequency noise has a deleterious impact on the observer. Extending one wide side of the rectangular nozzle, evocative of an aft deck in an installed propulsion system, increased the noise of the jet with increasing length. The impact of both aspect ratio and bevel length were relatively well behaved, allowing a simple bilinear model to be constructed relative to a simple round jet.
Numerical study on rectangular microhollow cathode discharge
He Shoujie; Ouyang Jiting; He Feng; Li Shang
2011-03-15
Rectangular microhollow cathode discharge in argon is investigated by using two-dimensional time-dependent self-consistent fluid model. The electric potential, electric field, particle density, and mean electron energy are calculated. The results show that hollow cathode effect can be onset in the present configuration, with strong electric field and high mean electron energy in the cathode fall while high density and quasineutral plasma in the negative glow. The potential well and electric filed reversal are formed in the negative glow region. It is suggested that the presence of large electron diffusion flux necessitates the field reversal and potential well.
Supersonic jets from bevelled rectangular nozzles
NASA Technical Reports Server (NTRS)
Rice, Edward J.; Raman, Ganesh
1993-01-01
The influence of nozzle exit geometry on jet mixing and noise production was studied experimentally for a series of rectangular nozzles operating at supersonic jet velocities. Both converging (C) and converging-diverging (C-D) nozzles were built with asymmetrical (single bevel) and symmetrical (double bevel) exit chambers and with conventional straight exits for comparison. About a four decibel reduction of peak mixing noise was observed for the double bevelled C-D nozzle operated at design pressure ratio. All bevelled geometries provided screech noise reduction for under-expanded jets and an upstream mixing noise directivity shift which would be beneficial for improved acoustic treatment performance of a shrouded system.
Recharge from rectangular areas to finite aquifers
NASA Astrophysics Data System (ADS)
Rao, N. H.; Sarma, P. B. S.
1981-10-01
A generalized analytical solution is derived for the growth of groundwater mound in finite aquifers bounded by open water bodies, in response to recharge from rectangular areas. Finite Fourier transforms are used to solve the linearized differential equation of groundwater flow. Unlike earlier solutions, the method presented here does not require the use of tables for evaluation of complicated functions. The solution is evaluated by comparison with existing numerical and analytical results. In stream-aquifer systems similar to those described above, application of the proposed solution is more realistic than using solutions available for infinite aquifers.
Steady evaporating flow in rectangular microchannels.
Griffiths, Stewart K.; Martinez, Mario J.; Tchikanda, Serge W.; Nilson, Robert H.
2005-02-01
Analytical and numerical solutions are presented for steady evaporating flow in open microchannels having a rectangular cross section and a uniform depth. The flow, driven by the axial gradient of capillary pressure, generally consists of an entry region where the meniscus is attached to the top corners of the channel followed by a jump-like transition to a corner-flow region in which the meniscus progressively recedes into the bottom corners of the channel. Illustrative numerical solutions are used to guide the derivation of an easily applied analytical approximation for the maximum sustainable heat flux or capillary limit.
Rectangular subsonic jet flow field measurements
NASA Technical Reports Server (NTRS)
Morrison, Gerald L.; Swan, David H.
1990-01-01
Flow field measurements of three subsonic rectangular cold air jets are presented. The three cases had aspect ratios of 1x2, 1x4 at a Mach number of 0.09 and an aspect ratio of 1x2 at a Mach number of 0.9. All measurements were made using a 3-D laser Doppler anemometer system. The data includes the mean velocity vector, all Reynolds stress tensor components, turbulent kinetic energy and velocity correlation coefficients. The data are presented in tabular and graphical form. No analysis of the measured data or comparison to other published data is made.
Flow-Field Surveys for Rectangular Nozzles
NASA Technical Reports Server (NTRS)
Zaman, K. B. M. Q.
2012-01-01
Flow field survey results for three rectangular nozzles are presented for a low subsonic condition obtained primarily by hot-wire anemometry. The three nozzles have aspect ratios of 2:1, 4:1 and 8:1. A fourth case included has 2:1 aspect ratio with chevrons added to the long edges. Data on mean velocity, turbulent normal and shear stresses as well as streamwise vorticity are presented covering a streamwise distance up to sixteen equivalent diameters from the nozzle exit. These detailed flow properties, including initial boundary layer characteristics, are usually difficult to measure in high speed flows and the primary objective of the study is to aid ongoing and future computational and noise modeling efforts.
Nonlinear vibrations of viscoelastic rectangular plates
NASA Astrophysics Data System (ADS)
Amabili, Marco
2016-02-01
Nonlinear vibrations of viscoelastic thin rectangular plates subjected to normal harmonic excitation in the spectral neighborhood of the lowest resonances are investigated. The von Kármán nonlinear strain-displacement relationships are used and geometric imperfections are taken into account. The material is modeled as a Kelvin-Voigt viscoelastic solid by retaining all the nonlinear terms. The discretized nonlinear equations of motion are studied by using the arclength continuation and collocation method. Numerical results are obtained for the fundamental mode of a simply supported square plate with immovable edges by using models with 16 and 22 degrees of freedom and investigating solution convergence. Comparison to viscous damping and the effect of neglecting nonlinear viscoelastic damping terms are shown. The change of the frequency-response with the retardation time parameter is also investigated as well as the effect of geometric imperfections.
Plasticity and rectangularity in survival curves
Weon, Byung Mook; Je, Jung Ho
2011-01-01
Living systems inevitably undergo a progressive deterioration of physiological function with age and an increase of vulnerability to disease and death. To maintain health and survival, living systems should optimize survival strategies with adaptive interactions among molecules, cells, organs, individuals, and environments, which arises plasticity in survival curves of living systems. In general, survival dynamics in a population is mathematically depicted by a survival rate, which monotonically changes from 1 to 0 with age. It would be then useful to find an adequate function to describe complicated survival dynamics. Here we describe a flexible survival function, derived from the stretched exponential function by adopting an age-dependent shaping exponent. We note that the exponent is associated with the fractal-like scaling in cumulative mortality rate. The survival function well depicts general features in survival curves; healthy populations exhibit plasticity and evolve towards rectangular-like survival curves, as examples in humans or laboratory animals. PMID:22355622
A transonic rectangular grid embedded panel method
NASA Technical Reports Server (NTRS)
Johnson, F. T.; Bussoletti, J. E.; James, R. M.; Young, D. P.; Woo, A. C.
1982-01-01
A method is presented that has the potential for solving transonic flow problems about the same complex aircraft configurations currently being analyzed by subsonic panel methods. This method does not require the generation of surface fitted grids. Instead it uses rectangular grids and subgrids together with embedded surface panels on which boundary conditions are imposed. Both the Euler and full potential equations are considered. The method of least squares is used to reduce the solution of these equations to the solution of a sequence of Poisson problems. The Poisson problems are solved using fast Fourier transforms and panel influence coefficient techniques. The overall method is still in its infancy but some two dimensional results are shown illustrating various key features.
The Lateral Instability of Deep Rectangular Beams
NASA Technical Reports Server (NTRS)
Dumont, C; Hill, H N
1937-01-01
Experimental and analytical studies were made of solid and hollow deep rectangular beams to study their lateral instability under various conditions of loading and restraint. The tests were made on bars and tubes of 17ST aluminum alloy. Failure by lateral buckling occurred only in tests on the solid beams. It was found that, within the elastic range, the test results were in agreement with the classical theory for the lateral buckling of deep beams as given by Prandtl, Mitchell, and Timoshenko. The tests were extended to the inelastic range, where it was found that the substitution for Young's modulus of an average modulus of elasticity derived from the stress-strain curve made it possible to predict instability at high stresses.
Rectangular subsonic jet flow field measurements
NASA Technical Reports Server (NTRS)
Morrison, Gerald L.; Swan, David H.
1989-01-01
Flow field measurements are presented of 3 subsonic rectangular cold air jets. The 3 cases presented had aspect ratios of 1 x 2, 1 x 4 at a Mach number of 0.09 and an aspect ratio of 1 x 2 at a Mach number of 0.9. All measurements were made using a 3-D laser Doppler anemoneter system. The presented data includes the mean velocity vector, all Reynolds stress tensor components, turbulent kinetic energy and velocity correlation coefficients. The data is presented in tabular and graphical form. No analysis of the measured data or comparison to other published data is made. All tabular data are available in ASCII format on MS-DOS compatible disks.
Magnetization reversal in single ferromagnetic rectangular nanowires
NASA Astrophysics Data System (ADS)
de Oliveira, Alexandre B.; da Silva, Gilvânia L.; Rezende, Sergio M.; Azevedo, Antonio
2010-01-01
We report on the magnetoresistance (MR) investigation of the magnetization reversal processes in single rectangular nanowire of Permalloy. A set of nanowires with lengths ranging from 6 to 20 μm, thicknesses fixed in 10 nm, and widths between 250 nm and 1.2 μm, was fabricated by means of AFM local anodic oxidation lithography. Magnetoresistive hysteresis loops show an abrupt jump corresponding to the magnetization reversal that depends on the angle between the wire axis and the applied magnetic field direction. The field value corresponding to the abrupt jump of the MR was associated to the nucleation field deduced from the Brown equations. By the angular dependence of this magnetization reversal field we were able to identify the nucleation mode as the magnetization buckling. We have investigated the temperature dependence of the switching field as well as its stochastic nature as a function of the in-plane angle.
Helping Students Acquainted with Multiplication in Rectangular Model
ERIC Educational Resources Information Center
Tasman, Fridgo; den Hertog, Jaap; Zulkardi; Hartono, Yusuf
2011-01-01
Usually, multiplication is introduced to students to represent quantities that come in groups. However there is also rectangular array model which is also related to multiplication. Barmby et al. (2009) has shown that the rectangular model such as array representations encourage students to develop their thinking about multiplication as a binary…
Method and structure for cache aware transposition via rectangular subsections
Gustavson, Fred Gehrung; Gunnels, John A
2014-02-04
A method and structure for transposing a rectangular matrix A in a computer includes subdividing the rectangular matrix A into one or more square submatrices and executing an in-place transposition for each of the square submatrices A.sub.ij.
Experimental Modal Analysis of Rectangular and Circular Beams
ERIC Educational Resources Information Center
Emory, Benjamin H.; Zhu, Wei Dong
2006-01-01
Analytical and experimental methods are used to determine the natural frequencies and mode shapes of Aluminum 6061-T651 beams with rectangular and circular cross-sections. A unique test stand is developed to provide the rectangular beam with different boundary conditions including clamped-free, clamped-clamped, clamped-pinned, and pinned-pinned.…
Development of the mean velocity distribution in rectangular jets
NASA Technical Reports Server (NTRS)
Morrison, G. L.; Swan, D. H.; Deotte, R. E., Jr.
1992-01-01
The mean flowfield of 1 x 2 and 1 x 4 aspect ratio rectangular jets has been measured using a laser Doppler anemometer system. The development of the downstream velocity distribution is analyzed with respect to centerline velocity decay, shear layer growth, axis switching, and velocity profile development. Comparisons are made with axisymmetric, planar, and other rectangular jets.
Residual Stress Measurement Using Rectangular Spiral Coils
NASA Astrophysics Data System (ADS)
Sun, Haiyan; Plotnikov, Yuri
2008-02-01
Shot peening process provides compressive residual stress within a depth of about 150˜200 um from the surface. It has been demonstrated that multi-frequency eddy current measurement can be effectively used for the residual stress estimation on Ni-based superalloys. In order to measure the stress profile over the entire compressive zone, the probe needs to work in a wide frequency range from 0.1 MHz to above 50 MHz. Due to its wide bandwidth and high precision fabrication process, spiral coils fabricated on flexible substrate using photolithographic technology are good candidate for this task It is useful to develop a coil model in order to optimize coil design, minimize liftoff effect and maximize coil gauge factor. In this work, a 3D analytical model was used to simulate rectangular spiral coil response on a half-space conductor. The results were compared with commercial available 3D finite element software and experimental results. The analytical model was also used to simulate 4-point calibration process that was used to calculate apparent eddy current conductivity (AECC). The experimental setup was described and AECC profile was obtained for shot-peening samples with different peening intensity and different heat treatment.
Perceptual guidelines for creating rectangular treemaps.
Kong, Nicholas; Heer, Jeffrey; Agrawala, Maneesh
2010-01-01
Treemaps are space-filling visualizations that make efficient use of limited display space to depict large amounts of hierarchical data. Creating perceptually effective treemaps requires carefully managing a number of design parameters including the aspect ratio and luminance of rectangles. Moreover, treemaps encode values using area, which has been found to be less accurate than judgments of other visual encodings, such as length. We conduct a series of controlled experiments aimed at producing a set of design guidelines for creating effective rectangular treemaps. We find no evidence that luminance affects area judgments, but observe that aspect ratio does have an effect. Specifically, we find that the accuracy of area comparisons suffers when the compared rectangles have extreme aspect ratios or when both are squares. Contrary to common assumptions, the optimal distribution of rectangle aspect ratios within a treemap should include non-squares, but should avoid extremes. We then compare treemaps with hierarchical bar chart displays to identify the data densities at which length-encoded bar charts become less effective than area-encoded treemaps. We report the transition points at which treemaps exhibit judgment accuracy on par with bar charts for both leaf and non-leaf tree nodes. We also find that even at relatively low data densities treemaps result in faster comparisons than bar charts. Based on these results, we present a set of guidelines for the effective use of treemaps and suggest alternate approaches for treemap layout. PMID:20975136
Film condensation in a horizontal rectangular duct
NASA Technical Reports Server (NTRS)
Lu, Qing; Suryanarayana, N. V.
1992-01-01
Condensation heat transfer in an annular flow regime with and without interfacial waves was experimentally investigated. The study included measurements of heat transfer rate with condensation of vapor flowing inside a horizontal rectangular duct and experiments on the initiation of interfacial waves in condensation, and adiabatic air-liquid flow. An analytical model for the condensation was developed to predict condensate film thickness and heat transfer coefficients. Some conclusions drawn from the study are that the condensate film thickness was very thin (less than 0.6 mm). The average heat transfer coefficient increased with increasing the inlet vapor velocity. The local heat transfer coefficient decreased with the axial distance of the condensing surface, with the largest change at the leading edge of the test section. The interfacial shear stress, which consisted of the momentum shear stress and the adiabatic shear stress, appeared to have a significant effect on the heat transfer coefficients. In the experiment, the condensate flow along the condensing surface experienced a smooth flow, a two-dimensional wavy flow, and a three-dimensional wavy flow. In the condensation experiment, the local wave length decreased with the axial distance of the condensing surface and the average wave length decreased with increasing inlet vapor velocity, while the wave speed increased with increasing vapor velocity. The heat transfer measurements are reliable. And, the ultrasonic technique was effective for measuring the condensate film thickness when the surface was smooth or had waves of small amplitude.
The hydrodynamic focusing effect inside rectangular microchannels
NASA Astrophysics Data System (ADS)
Lee, Gwo-Bin; Chang, Chih-Chang; Huang, Sung-Bin; Yang, Ruey-Jen
2006-05-01
This paper presents a theoretical and experimental investigation into the hydrodynamic focusing effect in rectangular microchannels. Two theoretical models for two-dimensional hydrodynamic focusing are proposed. The first model predicts the width of the focused stream in symmetric hydrodynamic focusing in microchannels of various aspect ratios. The second model predicts the location and the width of the focused stream in asymmetric hydrodynamic focusing in microchannels with a low or high aspect ratio. In both models, the theoretical results are shown to be in good agreement with the experimental data. Hence, the models provide a useful means of performing a theoretical analysis of flow control in microfluidic devices using hydrodynamic focusing effects. The ability of the proposed models to control the focused stream within a micro flow cytometer is verified in a series of experimental trials performed using polystyrene microparticles with a diameter of 20 µm. The experimental data show that the width of the focused stream can be reduced to the same order of magnitude as that of the particle size. Furthermore, it is shown that the microparticles can be successfully hydrodynamically focused and switched to the desired outlet port of the cytometer. Hence, the models presented in this study provide sufficient control to support cell/particle counting and sorting applications.
VIEW LOOKING NORTHEAST AT EARTH MOUND. NOTE THE RECTANGULAR OPENINGS ...
VIEW LOOKING NORTHEAST AT EARTH MOUND. NOTE THE RECTANGULAR OPENINGS USED FOR OBSERVATION EQUIPMENT AND PERISCOPE TOPS. - Marshall Space Flight Center, Redstone Rocket (Missile) Test Stand, Dodd Road, Huntsville, Madison County, AL
VIEW OF INTERIOR SPACE WITH RECTANGULAR SHAPE STRETCH PRESS CONTAINMENT ...
VIEW OF INTERIOR SPACE WITH RECTANGULAR SHAPE STRETCH PRESS CONTAINMENT PIT IN BACKGROUND, FACING NORTH. - Douglas Aircraft Company Long Beach Plant, Aircraft Parts Shipping & Receiving Building, 3855 Lakewood Boulevard, Long Beach, Los Angeles County, CA
Detail of ump that is attached to rectangular rearing tanks ...
Detail of ump that is attached to rectangular rearing tanks (pair). Pump located on the north end of rearing tank. View to the northwest. - Prairie Creek Fish Hatchery, Hwy. 101, Orick, Humboldt County, CA
Consensus dynamics on random rectangular graphs
NASA Astrophysics Data System (ADS)
Estrada, Ernesto; Sheerin, Matthew
2016-06-01
A random rectangular graph (RRG) is a generalization of the random geometric graph (RGG) in which the nodes are embedded into a rectangle with side lengths a and b = 1 / a, instead of on a unit square [ 0 , 1 ] 2. Two nodes are then connected if and only if they are separated at a Euclidean distance smaller than or equal to a certain threshold radius r. When a = 1 the RRG is identical to the RGG. Here we apply the consensus dynamics model to the RRG. Our main result is a lower bound for the time of consensus, i.e., the time at which the network reaches a global consensus state. To prove this result we need first to find an upper bound for the algebraic connectivity of the RRG, i.e., the second smallest eigenvalue of the combinatorial Laplacian of the graph. This bound is based on a tight lower bound found for the graph diameter. Our results prove that as the rectangle in which the nodes are embedded becomes more elongated, the RRG becomes a 'large-world', i.e., the diameter grows to infinity, and a poorly-connected graph, i.e., the algebraic connectivity decays to zero. The main consequence of these findings is the proof that the time of consensus in RRGs grows to infinity as the rectangle becomes more elongated. In closing, consensus dynamics in RRGs strongly depend on the geometric characteristics of the embedding space, and reaching the consensus state becomes more difficult as the rectangle is more elongated.
Passive Control of Supersonic Rectangular Jets through Boundary Layer Swirl
NASA Astrophysics Data System (ADS)
Han, Sang Yeop; Taghavi, Ray R.; Farokhi, Saeed
2013-06-01
Mixing characteristics of under-expanded supersonic jets emerging from plane and notched rectangular nozzles are computationally studied using nozzle exit boundary layer swirl as a mean of passive flow control. The coupling of the rectangular jet instability modes, such as flapping, and the swirl is investigated. A three-dimensional unsteady Reynolds-Averaged Navier-Stokes (RANS) code with shock adaptive grids is utilized. For plane rectangular nozzle with boundary layer swirl, the flapping and spanwise oscillations are captured in the jet's small and large dimensions at twice the frequencies of the nozzles without swirl. A symmetrical oscillatory mode is also observed in the jet with double the frequency of spanwise oscillation mode. For the notched rectangular nozzle with boundary layer swirl, the flapping oscillation in the small jet dimension and the spanwise oscillation in the large jet dimension are observed at the same frequency as those without boundary layer swirl. The mass flow rates in jets at 11 and 8 nozzle heights downstream of the nozzles increased by nearly 25% and 41% for the plane and notched rectangular nozzles respectively, due to swirl. The axial gross thrust penalty due to induced swirl was 5.1% for the plane and 4.9% for the notched rectangular nozzle.
Enhanced Mixing in a Rectangular Duct
NASA Technical Reports Server (NTRS)
Liscinsky, D. S.; True, B.
2003-01-01
An experimental investigation of the mixing of non-reacting opposed rows of jets injected normal to a confined rectangular crossflow has been conducted. Planar Mie-scattering was used to measure the time-average concentration distribution of the jet fluid in planes perpendicular to the duct axis. Particular emphasis was placed on the study of closely spaced orifice configurations applicable to the mixing zone of an RQL combustor. Baseline studies were performed of mixing under "ideal" conditions, i.e., plenum fed jets injecting into a crossflow uniform in velocity and turbulence intensity. In addition, more practical ("non-ideal") issues encountered during hardware design were also studied. As in other studies, mixing effectiveness, determined using a spatial unmixedness parameter based on the variance of mean jet concentration distributions, was found to be optimum when the spacing-to-duct-height ratio was inversely proportional to the square root of the jet-to-mainstream momentum-flux ratio. This relationship is suitable for design under ideal flow conditions. Inlet flow boundary conditions of the jet and approach flow (mainstream) were found to strongly influence mixing performance, but no attempt was made to determine optimum performance under non-ideal conditions. The tests performed do offer some guidance as to expected mixing behavior for several common variables likely to be imposed by hardware constraints. Additionally, in this study it was found that for rows of orifices with opposite centerlines inline, mixing was similar for blockages up to 89 percent (previous crossflow mixing studies concerned with dilution zone configurations, blockages were typically less than 50 percent). Lower levels of unmixedness were obtained as a function of downstream location when axial injection length was minimized. Mixing may be enhanced if orifice centerlines of opposed rows are staggered, but blockage must be =50 percent in this configuration. Round hole and "square
Corpectomy cage subsidence with rectangular versus round endcaps.
Deukmedjian, Armen R; Manwaring, Jotham; Le, Tien V; Turner, Alexander W L; Uribe, Juan S
2014-09-01
Corpectomy cages with rectangular endcaps utilize the stronger peripheral part of the endplate, potentially decreasing subsidence risk. The authors evaluated cage subsidence during cyclic biomechanical testing, comparing rectangular versus round endcaps. Fourteen cadaveric spinal segments (T12-L2) were dissected and potted at T12 and L2, then assigned to a rectangular (n=7) or round (n=7) endcap group. An L1 corpectomy was performed and under uniform conditions a cage/plate construct was cyclically tested in a servo-hydraulic frame with increasing load magnitude. Testing was terminated if the test machine actuator displacement exceeded 6mm, or the specimen completed cyclic loading at 2400 N. Number of cycles, compressive force and force-cycles product at test completion were all greater in the rectangular endcap group compared with the round endcap group (cycles: 3027 versus 2092 cycles; force: 1943 N versus 1533 N; force-cycles product: 6162kN·cycles versus 3973 kN·cycles), however these differences were not statistically significant (p ⩾ 0.076). After normalizing for individual specimen bone mineral density, the same measures increased to a greater extent with the rectangular endcaps (cycles: 3014 versus 1855 cycles; force: 1944 N versus 1444 N; force-cycles product: 6040 kN·cycles versus 2980 kN·cycles), and all differences were significant (p⩽0.030). The rectangular endcap expandable corpectomy cage displayed increased resistance to subsidence over the round endcap cage under cyclic loading as demonstrated by the larger number of cycles, maximum load and force-cycles product at test completion. This suggests rectangular endcaps will be less susceptible to subsidence than the round endcap design. PMID:24831343
Joining of Aluminium Alloy Sheets by Rectangular Mechanical Clinching
Abe, Y.; Mori, K.; Kato, T.
2011-05-04
A mechanical clinching has the advantage of low running costs. However, the joint strength is not high. To improve the maximum load of the joined sheets by a mechanical clinching, square and rectangular mechanical clinching were introduced. In the mechanical clinching, the two sheets are mechanically joined by forming an interlock between the lower and upper sheets by the punch and die. The joined length with the interlock was increased by the rectangular punch and die. The deforming behaviours of the sheets in the mechanical clinching were investigated, and then the interlock in the sheets had distribution in the circumference of the projection. Although the interlocks were formed in both projection side and diagonal, the interlock in the diagonal was smaller because of the long contact length between the lower sheet and the die cavity surface. The maximum load of the joined sheets by the rectangular mechanical clinching was two times larger than the load by the round mechanical clinching.
Dirichlet problem for equations of mixed type in rectangular domain
NASA Astrophysics Data System (ADS)
Basirovich, Sabitov Kamil
2015-11-01
In recent years, developed an interest in the study of boundary value problems for equations of mixed type in rectangular areas. This method proved theorems on the unique solubility and stability of the Dirichlet problem [1 - 3] under certain restrictions on the aspect ratio of the rectangular region of the hyperbolic. In this paper, for the mixed type equation with the Lavrent'ev-Bitsadze Dirichlet problem in a rectangular area. The criterion of uniqueness of the solution of the Dirichlet problem. The solution is built as the sum of the Fourier series. In justifying the convergence of a problem of small denominators regarding the relationship of the parties of the hyperbolic part of the rectangle. In connection with this evaluation are set to secede from scratch small denominator corresponding to the asymptotic behavior of rational and irrational values of the ratio, which allowed to substantiate the convergence of the series constructed in the class of regular solutions.
Simulation of multipactor on the rectangular grooved dielectric surface
NASA Astrophysics Data System (ADS)
Cai, Libing; Wang, Jianguo; Cheng, Guoxin; Zhu, Xiangqin; Xia, Hongfu
2015-11-01
Multipactor discharge on the rectangular grooved dielectric surface is simulated self-consistently by using a two-and-a-half dimensional (2.5 D) electrostatic particle-in-cell (PIC) code. Compared with the electromagnetic PIC code, the former can give much more accurate solution for the space charge field caused by the multipactor electrons and the deposited surface charge. According to the rectangular groove width and height, the multipactor can be divided into four models, the spatial distributions of the multipactor electrons and the space charge fields are presented for these models. It shows that the rectangular groove in different models gives very different suppression effect on the multipactor, effective and efficient suppression on the multipactor can only be reached with a proper groove size.
Resonance in cylindrical-rectangular and wraparound microstrip structures
NASA Technical Reports Server (NTRS)
Ali, Sami M.; Kong, Jin AU; Habashy, Tarek M.; Kiang, Jean-Fu
1989-01-01
A rigorous analysis of the resonance frequency problem of both the cylindrical-rectangular and the wraparound microstrip structure is presented. The problem is formulated in terms of a set of vector integral equations. Using Galerkin's method to solve the integral equations, the complex resonance frequencies are studied with sinusoidal basis functions which incorporate the edge singularity. The complex resonance frequencies are computed using a perturbation approach. Modes suitable for resonator or antenna applications are investigated. The edge singularity of the patch current is shown to have no significant effect on the accuracy of the results. It is shown that the HE10 modes of the cylindrical-rectangular and wraparound patches are more appropriate for resonator applications. The HE01 and TE01 modes of the cylindrical-rectangular and wraparound patches, respectively, are efficient radiating modes.
Simulation of multipactor on the rectangular grooved dielectric surface
Cai, Libing; Wang, Jianguo; Cheng, Guoxin; Zhu, Xiangqin; Xia, Hongfu
2015-11-15
Multipactor discharge on the rectangular grooved dielectric surface is simulated self-consistently by using a two-and-a-half dimensional (2.5 D) electrostatic particle-in-cell (PIC) code. Compared with the electromagnetic PIC code, the former can give much more accurate solution for the space charge field caused by the multipactor electrons and the deposited surface charge. According to the rectangular groove width and height, the multipactor can be divided into four models, the spatial distributions of the multipactor electrons and the space charge fields are presented for these models. It shows that the rectangular groove in different models gives very different suppression effect on the multipactor, effective and efficient suppression on the multipactor can only be reached with a proper groove size.
Prediction of radiative heat transfer in rectangular enclosures
Jamaluddin, A.S.; Smith, P.J.
1987-01-01
Discrete ordinates solutions of the radiative transport equation have been obtained for two- and three-dimensional rectangular enclosures using the S/sub 2/ and S/sub 4/ approximations. Limited evaluations indicate that both S/sub 2/ and S/sub 4/ are suitable for predicting radiative transfer in two-dimensional enclosures. However, for the three-dimensional enclosures the S/sub 2/ approximation is found inadequate. It is inferred that S/sub 4/ or higher order approximations should be used to accurately predict radiative heat transfer in three-dimensional rectangular enclosures.
Solves Poisson's Equation in Axizymmetric Geometry on a Rectangular Mesh
1996-09-10
DATHETA4.0 computes the magnetostatic field produced by multiple point current sources in the presence of perfect conductors in axisymmetric geometry. DATHETA4.0 has an interactive user interface and solves Poisson''s equation using the ADI method on a rectangular finite-difference mesh. DATHETA4.0 uncludes models specific to applied-B ion diodes.
Rectangular Array Model Supporting Students' Spatial Structuring in Learning Multiplication
ERIC Educational Resources Information Center
Shanty, Nenden Octavarulia; Wijaya, Surya
2012-01-01
We examine how rectangular array model can support students' spatial structuring in learning multiplication. To begin, we define what we mean by spatial structuring as the mental operation of constructing an organization or form for an object or set of objects. For that reason, the eggs problem was chosen as the starting point in which the…
Modal analysis applied to circular, rectangular, and coaxial waveguides
NASA Technical Reports Server (NTRS)
Hoppe, D. J.
1988-01-01
Recent developments in the analysis of various waveguide components and feedhorns using Modal Analysis (Mode Matching Method) are summarized. A brief description of the theory is presented, and the important features of the method are pointed out. Specific examples in circular, rectangular, and coaxial waveguides are included, with comparisons between the theory and experimental measurements. Extensions to the methods are described.
FDTD Analysis of U-Slot Rectangular Patch Antenna
NASA Technical Reports Server (NTRS)
Luk, K. M.; Tong, K. F.; Shum, S. M.; Lee, K. F.; Lee, R. Q.
1997-01-01
The U-slot rectangular patch antenna (Figure I) has been found experimentally to provide impedance and gain bandwidths of about 300 without the need of stacked or coplanar parasitic elements [1,2]. In this paper, simulation results of the U-slot patch using FDTD analysis are presented. Comparison with measured results are given.
The acoustic properties of panels with rectangular apertures.
Vigran, T E
2014-05-01
A model for the acoustic properties of a plate perforated with slots of rectangular shape is proposed. The model is based on known expressions for the complex density and compressibility of a pore of rectangular shape together with the radiation impedance of a rectangular shaped piston in a baffle. For the so-called end correction of a rectangular aperture in a plate, an approximate solution is shown to fit an exact solution for the imaginary part of the radiation impedance, the latter solution based on the work of Lindemann [J. Acoust. Soc. Am, 55, 708-717 (1974)]. Two different procedures are tested to calculate the mutual influence of the apertures on the end correction, the one calculating the mutual impedance of neighboring pistons in the plate, the other by calculating the end correction of a piston placed in the end of an infinitely long tube. The model is used calculating the input impedance and absorption coefficient of a Helmholtz resonator with such a plate, comparing with measurement results. The fit between predicted and measured results, using plates with narrow slits, is good, but it is believed that the model also cover a wider range of dimensions for such a slotted plate. PMID:24815260
New coplanar waveguide to rectangular waveguide end launcher
NASA Technical Reports Server (NTRS)
Simons, R. N.; Taub, S. R.
1992-01-01
A new coplanar waveguide to rectangular waveguide end launcher is experimentally demonstrated. The end launcher operates over the Ka-band frequencies that are designated for the NASA Advanced Communication Technology Satellite uplink. The measured insertion loss and return loss are better than 0.5 and -10 dB, respectively.
Rectangular-bore, high-gain laser plasma tube
NASA Technical Reports Server (NTRS)
Mollo, R. A.
1969-01-01
Rectangular-bore tube improves population inversion obtained from upper and terminal laser states, resulting in a significant increase in unsaturated gain factor. Radial field produces efficient pumping of upper laser state. Narrow tube dimensions cause increased diffusion flow of neon is metastable states to tube walls.
Gorman, Jhana; Hales, Jason Dean; Corona, Edmundo
2010-05-01
This report considers the calculation of the quasi-static nonlinear response of rectangular flat plates and tubes of rectangular cross-section subjected to compressive loads using quadrilateralshell finite element models. The principal objective is to assess the effect that the shell drilling stiffness parameter has on the calculated results. The calculated collapse load of elastic-plastic tubes of rectangular cross-section is of particular interest here. The drilling stiffness factor specifies the amount of artificial stiffness that is given to the shell element drilling Degree of freedom (rotation normal to the plane of the element). The element formulation has no stiffness for this degree of freedom, and this can lead to numerical difficulties. The results indicate that in the problems considered it is necessary to add a small amount of drilling tiffness to obtain converged results when using both implicit quasi-statics or explicit dynamics methods. The report concludes with a parametric study of the imperfection sensitivity of the calculated responses of the elastic-plastic tubes with rectangular cross-section.
Flow Through a Rectangular-to-Semiannular Diffusing Transition Duct
NASA Technical Reports Server (NTRS)
Foster, Jeff; Wendt, Bruce J.; Reichert, Bruce A.; Okiishi, Theodore H.
1997-01-01
Rectangular-to-semiannular diffusing transition ducts are critical inlet components on supersonic airplanes having bifucated engine inlets. This paper documents measured details of the flow through a rectangular-to-semiannular transition duct having an expansion area ratio of 1.53. Three-dimensional velocity vectors and total pressures at the exit plane of the diffuser are presented. Surface oil-flow visualization and surface static pressure data are shown. The tests were conducted with an inlet Mach number of 0.786 and a Reynolds number based on the inlet centerline velocity and exit diameter of 3.2 x 10(exp 6). The measured data are compared with previously published computational results. The ability of vortex generators to reduce circumferential total pressure distortion is demonstrated.
Lattice Boltzmann Equation On a 2D Rectangular Grid
NASA Technical Reports Server (NTRS)
Bouzidi, MHamed; DHumieres, Dominique; Lallemand, Pierre; Luo, Li-Shi; Bushnell, Dennis M. (Technical Monitor)
2002-01-01
We construct a multi-relaxation lattice Boltzmann model on a two-dimensional rectangular grid. The model is partly inspired by a previous work of Koelman to construct a lattice BGK model on a two-dimensional rectangular grid. The linearized dispersion equation is analyzed to obtain the constraints on the isotropy of the transport coefficients and Galilean invariance for various wave propagations in the model. The linear stability of the model is also studied. The model is numerically tested for three cases: (a) a vortex moving with a constant velocity on a mesh periodic boundary conditions; (b) Poiseuille flow with an arbitrasy inclined angle with respect to the lattice orientation: and (c) a cylinder &symmetrically placed in a channel. The numerical results of these tests are compared with either analytic solutions or the results obtained by other methods. Satisfactory results are obtained for the numerical simulations.
Analytical theory of an unloaded rectangular microstrip patch
NASA Astrophysics Data System (ADS)
Chang, D. C.
1981-01-01
A graphical method for determining the size of a resonant rectangular microstrip patch for a specified frequency is given. Using an expression obtained from the reflection coefficient of a transverse electromagnetic (TEM) wave in a semi-infinite microstrip patch, the resonance condition of a given mode for a patch of finite size is derived in a manner analogous to that of a rectangular, waveguide cavity. Radiation is shown to be in the form of both surface waves and space waves and is dependent on the angles of incidence for waves impinging onto the edges of the patch. By varying the aspect ratio, it is also possible to modify the Q factor of a resonant path. Analytical expressions for the resonant frequency and the Q factor are then derived under the assumption of a very thin substrate slab, encountered frequently in the application. Design curves in the form of the 'Argand diagram' are then presented for microstrip patches with fixed aspect ratios.
IR photodetector based on rectangular quantum wire in magnetic field
Jha, Nandan
2014-04-24
In this paper we study rectangular quantum wire based IR detector with magnetic field applied along the wires. The energy spectrum of a particle in rectangular box shows level repulsions and crossings when external magnetic field is applied. Due to this complex level dynamics, we can tune the spacing between any two levels by varying the magnetic field. This method allows user to change the detector parameters according to his/her requirements. In this paper, we numerically calculate the energy sub-band levels of the square quantum wire in constant magnetic field along the wire and quantify the possible operating wavelength range that can be obtained by varying the magnetic field. We also calculate the photon absorption probability at different magnetic fields and give the efficiency for different wavelengths if the transition is assumed between two lowest levels.
Intrinsic polarization control in rectangular GaN nanowire lasers
Li, Changyi; Liu, Sheng; Luk, Ting S.; Figiel, Jeffrey J.; Brener, Igal; Brueck, S. R. J.; Wang, George T.
2016-02-01
In this study, we demonstrate intrinsic, linearly polarized lasing from single GaN nanowires using cross-sectional shape control. A two-step top-down fabrication approach was employed to create straight nanowires with controllable rectangular cross-sections. A clear lasing threshold of 444kW/cm2 and a narrow spectral line width of 0.16 nm were observed under optical pumping at room temperature, indicating the onset of lasing. The polarization was along the short dimension (y-direction) of the nanowire due to the higher transverse confinement factors for y-polarized transverse modes resulting from the rectangular nanowire cross-section. The results show that cross-sectioned shape control can enable inherent control overmore » the polarization of nanowire lasers without additional environment requirements, such as placement onto lossy substrates.« less
Intrinsic polarization control in rectangular GaN nanowire lasers.
Li, Changyi; Liu, Sheng; Luk, Ting S; Figiel, Jeffrey J; Brener, Igal; Brueck, S R J; Wang, George T
2016-03-01
We demonstrate intrinsic, linearly polarized lasing from single GaN nanowires using cross-sectional shape control. A two-step top-down fabrication approach was employed to create straight nanowires with controllable rectangular cross-sections. A clear lasing threshold of 444 kW cm(-2) and a narrow spectral line width of 0.16 nm were observed under optical pumping at room temperature, indicating the onset of lasing. The polarization was along the short dimension (y-direction) of the nanowire due to the higher transverse confinement factors for y-polarized transverse modes resulting from the rectangular nanowire cross-section. The results show that cross-sectioned shape control can enable inherent control over the polarization of nanowire lasers without additional environment requirements, such as placement onto lossy substrates. PMID:26899502
Intrinsic polarization control in rectangular GaN nanowire lasers
NASA Astrophysics Data System (ADS)
Li, Changyi; Liu, Sheng; Luk, Ting. S.; Figiel, Jeffrey J.; Brener, Igal; Brueck, S. R. J.; Wang, George T.
2016-03-01
We demonstrate intrinsic, linearly polarized lasing from single GaN nanowires using cross-sectional shape control. A two-step top-down fabrication approach was employed to create straight nanowires with controllable rectangular cross-sections. A clear lasing threshold of 444 kW cm-2 and a narrow spectral line width of 0.16 nm were observed under optical pumping at room temperature, indicating the onset of lasing. The polarization was along the short dimension (y-direction) of the nanowire due to the higher transverse confinement factors for y-polarized transverse modes resulting from the rectangular nanowire cross-section. The results show that cross-sectioned shape control can enable inherent control over the polarization of nanowire lasers without additional environment requirements, such as placement onto lossy substrates.
Flexural rigidity of biaxially loaded reinforced concrete rectangular column sections
NASA Astrophysics Data System (ADS)
Resheidat, M.; Ghanma, M.; Sutton, C.; Chen, Wai-Fah
1995-05-01
An exact analysis is carried out utilizing the parabola-rectangle stress-strain curve for concrete and a typical idealized stress-strain curve for steel to develop the moment-curvature relationship for biaxially loaded reinforced concrete rectangular column sections. Based on that, the flexural rigidity EI of the section is determined at the yield curvature. A computer program is written by FORTRAN 77 to handle the required computations. The influence of material properties, the effect of steel ratios, and the impact of axial loads on the EI estimation were investigated. This study leads to the development of a new equation to estimate the flexural rigidity EI of reinforced concrete biaxially loaded rectangular columns in which these factors were considered. It is shown that the new equation stems from the actual behavior of the column. Therefore, it is recommended for general use in the design of slender columns.
Ground water quality assessment using multi-rectangular diagrams.
Ahmad, Niaz; Sen, Zekai; Ahmad, Manzoor
2003-01-01
A new graphical technique is proposed here for classifying chemical analyses of ground water. In this technique, a diagram is constructed using rectangular coordinates. The new diagram, called a multi-rectangular diagram (MRD), uses adjacent multi-rectangles in which each rectangle represents a specific ground water type. This new diagram has the capability to accommodate a large number of data sets. MRDs have been used to classify chemical analyses of ground water in the Chaj Doab area of Pakistan to illustrate this new approach. Using this graphical method, the differentiated ground water types are calcium bicarbonate, magnesium bicarbonate, sodium bicarbonate, and sodium sulfate. Sodium bicarbonate emerges as the most abundant ground water type. MRDs also offer a visual display of the Chebotarev sequence of ground water quality evolution. PMID:14649865
Comparison between different rectangular horn elements for array antenna applications
NASA Astrophysics Data System (ADS)
Lier, E.; Rengarjan, S.; Rahmat-Samii, Y.
1991-08-01
The coupling and directivity characteristics of an array with fundamental smooth-walled, soft and hard open-ended waveguide elements with rectangular cross-section are considered. Exact and approximate methods to analyze coupling in arrays are discussed. It is known that the coupling, which can be expressed by a quadruple integral across the rectangular apertures, can be reduced to double integrals by introducing a coordinate transformation. Calculations show that the soft waveguide elements are suited for applications where low return loss and mutual coupling are required. Arrays with hard waveguide elements yield high directivity for limited scan applications. Both elements can, in contrast to conventional smooth-walled (SW) horns, operate in dual polarization with high isolation between the orthogonal modes.
Partitioning Rectangular and Structurally Nonsymmetric Sparse Matrices for Parallel Processing
B. Hendrickson; T.G. Kolda
1998-09-01
A common operation in scientific computing is the multiplication of a sparse, rectangular or structurally nonsymmetric matrix and a vector. In many applications the matrix- transpose-vector product is also required. This paper addresses the efficient parallelization of these operations. We show that the problem can be expressed in terms of partitioning bipartite graphs. We then introduce several algorithms for this partitioning problem and compare their performance on a set of test matrices.
Real time rectangular document detection on mobile devices
NASA Astrophysics Data System (ADS)
Skoryukina, Natalya; Nikolaev, Dmitry P.; Sheshkus, Alexander; Polevoy, Dmitry
2015-02-01
In this paper we propose an algorithm for real-time rectangular document borders detection in mobile device based applications. The proposed algorithm is based on combinatorial assembly of possible quadrangle candidates from a set of line segments and projective document reconstruction using the known focal length. Fast Hough Transform is used for line detection. 1D modification of edge detector is proposed for the algorithm.
Propagation of a low-frequency rectangular pulse in seawater
NASA Astrophysics Data System (ADS)
King, Ronold W. P.
1993-05-01
As a necessary preliminary to the determination of the electromagnetic field scattered by a metal cylinder submerged in the ocean, the propagation of a low frequency pulse with a rectangular envelope is evaluated numerically as a function of the distance of travel. Graphs of the three component terms and their sum are shown for four distances. The very significant changes in shape and amplitude of the pulse are discussed.
The hydrodynamic advantages of synchronized swimming in a rectangular pattern.
Daghooghi, Mohsen; Borazjani, Iman
2015-10-01
Fish schooling is a remarkable biological behavior that is thought to provide hydrodynamic advantages. Theoretical models have predicted significant reduction in swimming cost due to two physical mechanisms: vortex hypothesis, which reduces the relative velocity between fish and the flow through the induced velocity of the organized vortex structure of the incoming wake; and the channeling effect, which reduces the relative velocity by enhancing the flow between the swimmers in the direction of swimming. Although experimental observations confirm hydrodynamic advantages, there is still debate regarding the two mechanisms. We provide, to our knowledge, the first three-dimensional simulations at realistic Reynolds numbers to investigate these physical mechanisms. Using large-eddy simulations of self-propelled synchronized swimmers in various rectangular patterns, we find evidence in support of the channeling effect, which enhances the flow velocity between swimmers in the direction of swimming as the lateral distance between swimmers decreases. Our simulations show that the coherent structures, in contrast to the wake of a single swimmer, break down into small, disorganized vortical structures, which have a low chance for constructive vortex interaction. Therefore, the vortex hypothesis, which is relevant for diamond patterns, was not found for rectangular patterns, but needs to be further studied for diamond patterns in the future. Exploiting the channeling mechanism, a fish in a rectangular school swims faster as the lateral distance decreases, while consuming similar amounts of energy. The fish in the rectangular school with the smallest lateral distance (0.3 fish lengths) swims 20% faster than a solitary swimmer while consuming similar amount of energy. PMID:26447493
Radial Eigenmodes for a Toroidal Waveguide with Rectangular Cross Section
Rui Li
2012-07-01
In applying mode expansion to solve the CSR impedance for a section of toroidal vacuum chamber with rectangular cross section, we identify the eigenvalue problem for the radial eigenmodes which is different from that for cylindrical structures. In this paper, we present the general expressions of the radial eigenmodes, and discuss the properties of the eigenvalues on the basis of the Sturm-Liouville theory.
Bandwidth Study of the Microwave Reflectors with Rectangular Corrugations
NASA Astrophysics Data System (ADS)
Zhang, Liang; He, Wenlong; Donaldson, Craig R.; Cross, Adrian W.
2016-09-01
The mode-selective microwave reflector with periodic rectangular corrugations in the inner surface of a circular metallic waveguide is studied in this paper. The relations between the bandwidth and reflection coefficient for different numbers of corrugation sections were studied through a global optimization method. Two types of reflectors were investigated. One does not consider the phase response and the other does. Both types of broadband reflectors operating at W-band were machined and measured to verify the numerical simulations.
Augmented Beta rectangular regression models: A Bayesian perspective.
Wang, Jue; Luo, Sheng
2016-01-01
Mixed effects Beta regression models based on Beta distributions have been widely used to analyze longitudinal percentage or proportional data ranging between zero and one. However, Beta distributions are not flexible to extreme outliers or excessive events around tail areas, and they do not account for the presence of the boundary values zeros and ones because these values are not in the support of the Beta distributions. To address these issues, we propose a mixed effects model using Beta rectangular distribution and augment it with the probabilities of zero and one. We conduct extensive simulation studies to assess the performance of mixed effects models based on both the Beta and Beta rectangular distributions under various scenarios. The simulation studies suggest that the regression models based on Beta rectangular distributions improve the accuracy of parameter estimates in the presence of outliers and heavy tails. The proposed models are applied to the motivating Neuroprotection Exploratory Trials in Parkinson's Disease (PD) Long-term Study-1 (LS-1 study, n = 1741), developed by The National Institute of Neurological Disorders and Stroke Exploratory Trials in Parkinson's Disease (NINDS NET-PD) network. PMID:26289406
Two-Channel Rectangular Dielectric Wake Field Accelerator Structure Experiment
Sotnikov, G. V.; Marshall, T. C.; Shchelkunov, S. V.; Didenko, A.; Hirshfield, J. L.
2009-01-22
A design is presented for a two-channel 30-GHz rectangular dielectric wake field accelerator structure being built for experimental tests at Argonne National Laboratory (ANL). This structure allows for a transformer ratio T much greater than two, and permits continuous coupling of energy from drive bunches to accelerated bunches. It consists of three planar slabs of cordierite ceramic ({epsilon} = 4.7) supported within a rectangular copper block, forming a drive channel 12 mmx6 mm, and an accelerator channel 2 mmx6 mm. When driven by a 50 nC, 14 MeV single bunch available at ANL, theory predicts an acceleration field of 6 MeV/m, and T = 12.6. Inherent transverse wake forces introduce deflections and some distortion of bunch profiles during transit through the structure that are estimated to be tolerable. Additionally, a cylindrical two-channel DWFA is introduced which shares many advantages of the rectangular structure including high T, and the added virtue of axisymmetry that eliminates lowest-order transverse deflecting forces.
Free vibration of rectangular plates with a small initial curvature
NASA Technical Reports Server (NTRS)
Adeniji-Fashola, A. A.; Oyediran, A. A.
1988-01-01
The method of matched asymptotic expansions is used to solve the transverse free vibration of a slightly curved, thin rectangular plate. Analytical results for natural frequencies and mode shapes are presented in the limit when the dimensionless bending rigidity, epsilon, is small compared with in-plane forces. Results for different boundary conditions are obtained when the initial deflection is: (1) a polynomial in both directions, and (2) the product of a polynomial and a trigonometric function, and arbitrary. For the arbitrary initial deflection case, the Fourier series technique is used to define the initial deflection. The results obtained show that the natural frequencies of vibration of slightly curved plates are coincident with those of perfectly flat, prestressed rectangular plates. However, the eigenmodes are very different from those of initially flat prestressed rectangular plates. The total deflection is found to be the sum of the initial deflection, the deflection resulting from the solution of the flat plate problem, and the deflection resulting from the static problem.
The pulsating laminar flow in a rectangular channel
NASA Astrophysics Data System (ADS)
Valueva, E. P.; Purdin, M. S.
2015-11-01
The finite difference method is used to solve the task of the developed pulsating laminar flow in a rectangular channel. The optimum of the difference scheme parameters was determined. Data on the amplitude and phase of the longitudinal velocity oscillations, the hydraulic and friction drag coefficients, the shear stress on the wall have been obtained. Using the dimensionless value of the frequency pulsations two characteristic regimes — the quasisteady-state regime and the high-frequency regime have been identified. In the quasi-steady-state regime, the values of all hydrodynamic quantities at each instant of time correspond to the velocity value averaged over the cross section at a given moment of time. It is shown that in the high-frequency regime, the dependences on the dimensionless oscillation frequency of oscillating components of hydrodynamic quantities are identical for rectilinear channels with a different cross-sectional form (round pipe, flat and a rectangular channels). The effect of the aspect ratio of the rectangular channel sides channel on the pulsating flow dynamics has been analyzed.
Single and Multi-channel Quantum Dragons from Rectangular Nanotubes
NASA Astrophysics Data System (ADS)
Li, Zhou; Novotny, Mark
2015-03-01
Recently quantum dragons have been discovered theoretically. Quantum dragons are nanostructures with correlated disorder that permit energy-independent total quantum transmission of electrons. Hence the electrical conductance G in a two-terminal measurement should be the conductance quantum G0 = 2e2 / h . The single-band tight banding model is used. An example of a single-channel quantum dragon is a rectangular nanotube with disorder along the direction z of the electron propagation. Quantum dragons are obtained by solving the time-independent Schrödinger equation to obtain the electrical transmission calT as a function of the incoming electron energy E. A quantum dragon has calT (E) =1 for all energies. This work generalizes the solution of the time-independent Schrödinger equation to the case of more than one open channel, and applies the method to nanotubes formed from rectangular lattices. One can envision such single-walled rectangular nanotubes for iron starting from free-standing single-atom-thick Fe membranes which have recently been obtained experimentally. Supported in part by NSF Grant DMR-1206233.
RWGSCAT/CWGSCAT - RECTANGULAR AND CIRCULAR WAVEGUIDE JUNCTION SCATTERING PACKAGE
NASA Technical Reports Server (NTRS)
Hoppe, D. J.
1994-01-01
Accurate computer modeling of passive circular or rectangular waveguide components is often required during the design phase for optimizing frequency response and/or determining the tolerance required on components in order to meet radio frequency specifications. RWGSCAT/CWGSCAT is capable of modeling both types of waveguide components. The Scattering Matrix Program for Circular Waveguide Junctions, CWGSCAT, computes the scattering matrix for a circular waveguide. This includes a dual mode horn and certain types of corrugated horns. RWGSCAT, Rectangular WaveGuide junction SCATtering program, solves for the scattering properties of a rectangular waveguide device, such as a smooth or corrugated rectangular horn, step transformer, or filter. RWGSCAT and CWGSCAT are also available separately as NPO-19091 and NPO-18708, respectively. Many circular waveguide devices can be represented either exactly or approximately as a series of circular waveguide sections which have a common center. In addition, smooth tapers and horns of arbitrary profile may be approximated by a series of small steps. Devices that may be analyzed in this fashion include a simple waveguide step discontinuity, such as that used in a dual mode horn, a stepped matching section, or a corrugated waveguide section with constant varying slot depth. CWGSCAT will accurately predict the reflection and transmission characteristics of such devices, taking into account higher order mode excitation if it occurs as well as multiple reflections and stored energy at each discontinuity. For large devices, with respect to a wavelength where many modes may propagate, the reflection and transmission properties may be required for a higher order mode or series of modes exciting the device. Such interactions are represented best by defining a scattering matrix for the device. The matrix can be determined by using mode matching at each discontinuity present. The results for individual discontinuities are then cascaded to
Investigation of imaging properties for submillimeter rectangular pinholes
Xia, Dan; Moore, Stephen C. E-mail: miaepark@bwh.harvard.edu Park, Mi-Ae E-mail: miaepark@bwh.harvard.edu Cervo, Morgan E-mail: miaepark@bwh.harvard.edu; Metzler, Scott D.
2015-12-15
Purpose: Recently, a multipinhole collimator with inserts that have both rectangular apertures and rectangular fields of view (FOVs) has been proposed for SPECT imaging since it can tile the projection onto the detector efficiently and the FOVs in transverse and axial directions become separable. The purpose of this study is to investigate the image properties of rectangular-aperture pinholes with submillimeter apertures sizes. Methods: In this work, the authors have conducted sensitivity and FOV experiments for 18 replicates of a prototype insert fabricated in platinum/iridium (Pt/Ir) alloy with submillimeter square-apertures. A sin{sup q}θ fit to the experimental sensitivity has been performed for these inserts. For the FOV measurement, the authors have proposed a new formula to calculate the projection intensity of a flood image on the detector, taking into account the penumbra effect. By fitting this formula to the measured projection data, the authors obtained the acceptance angles. Results: The mean (standard deviation) of fitted sensitivity exponents q and effective edge lengths w{sub e} were, respectively, 10.8 (1.8) and 0.38 mm (0.02 mm), which were close to the values, 7.84 and 0.396 mm, obtained from Monte Carlo calculations using the parameters of the designed inserts. For the FOV measurement, the mean (standard deviation) of the transverse and axial acceptances were 35.0° (1.2°) and 30.5° (1.6°), which are in good agreement with the designed values (34.3° and 29.9°). Conclusions: These results showed that the physical properties of the fabricated inserts with submillimeter aperture size matched our design well.
Sloshing roof impact tests of a rectangular tank
NASA Astrophysics Data System (ADS)
Minowa, Chikahiro; Ogawa, Nobuyuki; Harada, Iki; Ma, David C.
Some tanks have been damaged at the roofs due to sloshing impact caused by strong earthquakes. It is, therefore, necessary to consider the impact force in the aseismic design code for tank roofs. However, there are few studies on the earthquake responses of storage and process tank roofs. As a first step to investigate the effects of sloshing impact a series of the shaking table tests of a rectangular tank have been conducted at the National Research Institute for Earth Science and Disaster Prevention (NIED). The results of these shaking table tests are presented in the paper. The test tank is rectangular in shape having dimensions of 5 m x 3 m x 2 m (length x width x height). The tank was constructed of glass-fiber reinforced plastic panels. Every panel had a flange on four edges, and each panel was connected by bolts along the flange. The test tank was set on the NIED shaking table (15 m by 15 m). Two types of liquid were used, water and a viscous liquid (water mixed with polymeric powders). The roof impact pressures and other quantities were measured. During the tests using the 400 pi El-Centro excitation, the roof deformation sensor steel beam was damaged. The response of side walls with different rigidity were measured in the wall bulging tests. The measured vibrations within the panel plates were larger than those in the panel flanges. The viscous liquid of 100 cp had little influence on wall bulging responses. However, the viscous effects on sloshing responses were observed in the sloshing tests. Approximate analyses of rectangular tanks, considering the influence of static water pressure, are also presented in this paper.
Sloshing roof impact tests of a rectangular tank
Minowa, C.; Ogawa, N.; Harada, I.; Ma, D.C.
1994-06-01
Some tanks have been damaged at the roofs due to sloshing impact caused by strong earthquakes. It is, therefore, necessary to consider the impact force in the aseismic design code for tank roofs. However, there are few studies on the earthquake responses of storage and process tank roofs. As a first step to investigate the effects of sloshing impact a series of the shaking table tests of a rectangular tank have been conducted at the National Research Institute for Earth Science and Disaster Prevention (NIED). The results of these shaking table tests are presented in the paper. The test tank is rectangular in shape having dimensions of 5 m {times} 3 m {times} 2 m length {times} width {times} height). The tank was constructed of glass-fiber reinforced plastic panels. Every panel had a flange on four edges, and each panel was connected by bolts along the flange. The test tank was set on the NIED shaking table (15 m by 15 m). Two types of liquid were used, water and a viscous liquid (water mixed with polymeric powders). The roof impact pressures and other quantities were measured. During the tests using the 400 pi El-Centro excitation, the roof deformation sensor steel beam was damaged. The response of side walls with different rigidity were measured in the wall bulging tests. The measured vibrations within the panel plates were larger than those in the panel flanges. The viscous liquid of 100 cp had little influence on wall bulging responses. However, the viscous effects on sloshing responses were observed in the sloshing tests. Approximate analyses of rectangular tanks, considering the influence of static water pressure, are also presented in this paper.
Microwave corrosion detection using open ended rectangular waveguide sensors
Qaddoumi, N.; Handjojo, L.; Bigelow, T.; Easter, J.; Bray, A.; Zoughi, R.
2000-02-01
The use of microwave and millimeter wave nondestructive testing methods utilizing open ended rectangular waveguide sensors has shown great potential for detecting minute thickness variations in laminate structures, in particular those backed by a conducting plate. Slight variations in the dielectric properties of materials may also be detected using a set of optimal parameters which include the standoff distance and the frequency of operation. In a recent investigation, on detecting rust under paint, the dielectric properties of rust were assumed to be similar to those of Fe{sub 2}O{sub 3} powder. These values were used in an electromagnetic model that simulates the interaction of fields radiated by a rectangular waveguide aperture with layered structures to obtain optimal parameters. The dielectric properties of Fe{sub 2}O{sub 3} were measured to be very similar to the properties of paint. Nevertheless, the presence of a simulated Fe{sub 2}O{sub 3} layer under a paint layer was detected. In this paper the dielectric properties of several different rust samples from different environments are measured. The measurements indicate that the nature of real rust is quite diverse and is different from Fe{sub 2}O{sub 3} and paint, indicating that the presence of rust under paint can be easily detected. The same electromagnetic model is also used (with the newly measured dielectric properties of real rust) to obtain an optimal standoff distance at a frequency of 24 GHz. The results indicate that variations in the magnitude as well as the phase of the reflection coefficient can be used to obtain information about the presence of rust. An experimental investigation on detecting the presence of very thin rust layers (2.5--5 x 10{sup {minus}2} mm [09--2.0 x 10{sup {minus}3} in.]) using an open ended rectangular waveguide probe is also conducted. Microwave images of rusted specimens, obtained at 24 GHz, are also presented.
Rectangular Array Of Digital Processors For Planning Paths
NASA Technical Reports Server (NTRS)
Kemeny, Sabrina E.; Fossum, Eric R.; Nixon, Robert H.
1993-01-01
Prototype 24 x 25 rectangular array of asynchronous parallel digital processors rapidly finds best path across two-dimensional field, which could be patch of terrain traversed by robotic or military vehicle. Implemented as single-chip very-large-scale integrated circuit. Excepting processors on edges, each processor communicates with four nearest neighbors along paths representing travel to north, south, east, and west. Each processor contains delay generator in form of 8-bit ripple counter, preset to 1 of 256 possible values. Operation begins with choice of processor representing starting point. Transmits signals to nearest neighbor processors, which retransmits to other neighboring processors, and process repeats until signals propagated across entire field.
Corner heating in rectangular solid oxide electrochemical cell generators
Reichner, Philip
1989-01-01
Disclosed is an improvement in a solid oxide electrochemical cell generator 1 having a rectangular design with four sides that meet at corners, and containing multiplicity of electrically connected fuel cells 11, where a fuel gas is passed over one side of said cells and an oxygen containing gas is passed into said cells, and said fuel is burned to form heat, electricity, and an exhaust gas. The improvement comprises passing the exhaust gases over the multiplicity of cells 11 in such a way that more of the heat in said exhaust gases flows at the corners of the generator, such as through channels 19.
Damage Analysis of Rectangular Section Composite Beam under Pure Bending
NASA Astrophysics Data System (ADS)
Liu, Yiping; Xiao, Fan; Liu, Zejia; Tang, Liqun; Fang, Daining
2013-02-01
Laminated composite beams are commonly used in engineering applications involving macro to nano structures. Based on the assumption that plain sections remain plain after deformation, this paper analyzes stress distributions in cross-ply laminated composite beams with rectangular cross-sections, and formulates the basic damage equations through Kachanov's damage definition and Janson's failure criterion. The location of the neutral axis and the ultimate bending moment are obtained for pure bending cases. The effect of the elastic modulus of the two layers on the damage evolution is analyzed; a reasonable damage composite beam model is proposed to predict the ultimate bending moment.
The Gross-Pitaevskii Hierarchy on General Rectangular Tori
NASA Astrophysics Data System (ADS)
Herr, Sebastian; Sohinger, Vedran
2016-06-01
In this work, we study the Gross-Pitaevskii hierarchy on general—rational and irrational—rectangular tori of dimensions two and three. This is a system of infinitely many linear partial differential equations which arises in the rigorous derivation of the nonlinear Schrödinger equation. We prove a conditional uniqueness result for the hierarchy. In two dimensions, this result allows us to obtain a rigorous derivation of the defocusing cubic nonlinear Schrödinger equation from the dynamics of many-body quantum systems. On irrational tori, this question was posed as an open problem in the previous work of Kirkpatrick, Schlein, and Staffilani.
Modeling of a nanoscale rectangular hole in a real metal.
Kumar, Arun; Srivastava, Triranjita
2008-02-15
We propose and implement a simple and accurate method to analyze a subwavelength rectangular hole in a real metal and obtain the modal characteristics of its fundamental mode. Our results are found to be in excellent agreement with those reported in the literature, obtained by the effective index method (EIM) and finite-element and finite-difference methods. Unlike the EIM, the present method has no ambiguity in its implementation and is able to predict the major field components also, which may be useful in understanding the extraordinary transmission characteristics of such structures. PMID:18278101
Width effects in transonic flow over a rectangular cavity
Beresh, Steven J.; Wagner, Justin L.; Henfling, John F.; Spillers, Russell Wayne; Pruett, Brian Owen Matthew
2015-07-24
A previous experiment by the present authors studied the flow over a finite-width rectangular cavity at freestream Mach numbers 1.5–2.5. In addition, this investigation considered the influence of three-dimensional geometry that is not replicated by simplified cavities that extend across the entire wind-tunnel test section. The latter configurations have the attraction of easy optical access into the depths of the cavity, but they do not reproduce effects upon the turbulent structures and acoustic modes due to the length-to-width ratio, which is becoming recognized as an important parameter describing the nature of the flow within narrower cavities.
Extending the MODPATH Algorithm to Rectangular Unstructured Grids.
Pollock, David W
2016-01-01
The recent release of MODFLOW-USG, which allows model grids to have irregular, unstructured connections, requires a modification of the particle-tracking algorithm used by MODPATH. This paper describes a modification of the semi-analytical particle-tracking algorithm used by MODPATH that allows it to be extended to rectangular-based unstructured grids by dividing grid cells with multi-cell face connections into sub-cells. The new method will be incorporated in the next version of MODPATH which is currently under development. PMID:25754305
A New Fuzzy System Based on Rectangular Pyramid
Jiang, Mingzuo; Yuan, Xuehai; Li, Hongxing; Wang, Jiaxia
2015-01-01
A new fuzzy system is proposed in this paper. The novelty of the proposed system is mainly in the compound of the antecedents, which is based on the proposed rectangular pyramid membership function instead of t-norm. It is proved that the system is capable of approximating any continuous function of two variables to arbitrary degree on a compact domain. Moreover, this paper provides one sufficient condition of approximating function so that the new fuzzy system can approximate any continuous function of two variables with bounded partial derivatives. Finally, simulation examples are given to show how the proposed fuzzy system can be effectively used for function approximation. PMID:25874253
3-D LDA study of a rectangular jet
NASA Technical Reports Server (NTRS)
Morrison, Gerald L.; Tatterson, Gary B.; Swan, David H.
1988-01-01
The flow field of a rectangular jet with a 2:1 aspect ratio was studied at an axial Reynolds number of 100,000 (Mach number 0.09) using three-dimensional laser Doppler velocimetry. The flow field survey resulted in mean velocity vector field plots and contour plots of the Reynolds stress tensor components. This paper presents contour plots in the planes of the jet minor and major axes at different axial locations. These data contribute substantially to currently available data of jet flow fields and will provide a valuable database for three-dimensional modeling.
Acoustic response of a rectangular levitator with orifices
NASA Technical Reports Server (NTRS)
El-Raheb, Michael; Wagner, Paul
1990-01-01
The acoustic response of a rectangular cavity to speaker-generated excitation through waveguides terminating at orifices in the cavity walls is analyzed. To find the effects of orifices, acoustic pressure is expressed by eigenfunctions satisfying Neumann boundary conditions as well as by those satisfying Dirichlet ones. Some of the excess unknowns can be eliminated by point constraints set over the boundary, by appeal to Lagrange undetermined multipliers. The resulting transfer matrix must be further reduced by partial condensation to the order of a matrix describing unmixed boundary conditions. If the cavity is subjected to an axial temperature dependence, the transfer matrix is determined numerically.
Crack problems for a rectangular plate and an infinite strip
NASA Technical Reports Server (NTRS)
Civelek, M. B.; Erdogan, F.
1980-01-01
The general plane problem for an infinite strip containing multiple cracks perpendicular to its boundaries is considered. The problem is reduced to a system of singular integral equations. Two specific problems of practical interest are then studied in detail. The first problem explores the interaction effect of multiple edge cracks in a plate or beam under tension or bending. The second problem is that of a rectangular plate containing an arbitrarily oriented crack in the plane of symmetry. Particular emphasis is placed on the problem of a plate containing an edge crack and subjected to concentrated forces.
Stresses Around Rectangular Cut-outs with Reinforced Coaming Stringers
NASA Technical Reports Server (NTRS)
Kuhn, Paul; Rafel, Norman; Griffith, George E
1947-01-01
Strain measurements and strength tests were made on six skin-stringer panels under axial load. Three of these panels had short rectangular cut-outs, and three a long one. The width of the cut-out was about one-half of the width of the panel. Three types of coating stringers were used: without reinforcement, with riveted-up reinforcement, or with integral reinforcement. The strain measurements were found to be in good agreement with a previously published theory adapted where necessary by making overlapping assumptions.
Nonlinear dynamics and control of a vibrating rectangular plate
NASA Technical Reports Server (NTRS)
Shebalin, J. V.
1983-01-01
The von Karman equations of nonlinear elasticity are solved for the case of a vibrating rectangular plate by meams of a Fourier spectral transform method. The amplification of a particular Fourier mode by nonlinear transfer of energy is demonstrated for this conservative system. The multi-mode system is reduced to a minimal (two mode) system, retaining the qualitative features of the multi-mode system. The effect of a modal control law on the dynamics of this minimal nonlinear elastic system is examined.
Nonlinear analysis of the dielectric loaded rectangular Cerenkov maser
NASA Astrophysics Data System (ADS)
Zhao, Ding; Ding, Yaogen
2012-02-01
To deeply investigate the nonlinear interaction between the sheet beam and the slow wave mode in the dielectric loaded rectangular Cerenkov maser, a third order differential equation of the field profile function is rigorously derived. By combining with the relativistic equation of motion and using the traveling-wave boundary condition, the nonlinear phenomena, which involve with the growth rate, the electron phase bunching, the saturated power and length, etc., can be predicted through numerical calculations. An illustrative example has been given to demonstrate the validation of this method. The results show that a beam with axial momentum spread will lower the saturated power, increase the saturated length, and decrease the working bandwidth.
Extending the MODPATH algorithm to rectangular unstructured grids
Pollock, David W.
2016-01-01
The recent release of MODFLOW-USG, which allows model grids to have irregular, unstructured connections, requires a modification of the particle-tracking algorithm used by MODPATH. This paper describes a modification of the semi-analytical particle-tracking algorithm used by MODPATH that allows it to be extended to rectangular-based unstructured grids by dividing grid cells with multi-cell face connections into sub-cells. The new method will be incorporated in the next version of MODPATH which is currently under development.
RHCP- DESIGNING RECTANGULAR RIGHT-HANDED CIRCULARLY POLARIZED MICROSTRIP ANTENNAS
NASA Technical Reports Server (NTRS)
Davidson, S. E.
1994-01-01
RHCP, the Right-Handed, Circularly Polarized Microstrip Antenna program, aids in the design of a rectangular antenna element, given the desired frequency of operation and substrate characteristics. RHCP begins the design calculations based on a square element with linear polarization. The effective dielectric constant and changes in electrical length due to fringing at the radiating element edges are taken into account. A coaxial feed is inset with 50 ohms input impedance. By placing the feed such that two orthonormal modes are produced in the antenna cavity, right- or left-handed circular polarization is obtained. Input to RHCP consists of desired frequency, dielectric constant, and substrate thickness. Output consists of the final rectangular geometry, the proposed feed inset placement, and actual input impedance. RHCP has been used successfully for frequencies between 2 and 15 GHz for thin substrates. This program was used to fabricate antenna elements for the S-band quad antennas on board the Space Shuttle, and is a part of the design project for the S-band phased array antenna radiating aperture. RHCP is written in FORTRAN 77 for interactive execution and has been implemented on a DEC VAX series computer operating under VMS. This program was developed in 1985.
Sampling requirements for forage quality characterization of rectangular hay bales
Sheaffer, C.C.; Martin, N.P.; Jewett, J.G.; Halgerson, J.; Moon, R.D.; Cuomo, G.R.
2000-02-01
Commercial lots of alfalfa (Medicago sativa L.) hay are often bought and sold on the basis of forage quality. Proper sampling is essential to obtain accurate forage quality results for pricing of alfalfa hay, but information about sampling is limited to small, 20- to 40-kg rectangular bales. Their objectives were to determine the within-bale variation in 400-kg rectangular bales and to determine the number and distribution of core samples required to represent the crude protein (CP), acid detergent fiber (ADF), neutral detergent fiber (NDF), and dry matter (DM) concentration in commercial lots of alfalfa hay. Four bales were selected from each of three hay lots and core sampled nine times per side for a total of 54 cores per bale. There was no consistent pattern of forage quality variation within bales. Averaged across lots, any portion of a bale was highly correlated with bale grand means for CP, ADF, NDF, and DM. Three lots of hay were probed six times per bale, one core per bale side from 55, 14, and 14 bales per lot. For determination of CP, ADF, NDF, and DM concentration, total core numbers required to achieve an acceptable standard error (SE) were minimized by sampling once per bale. Bootstrap analysis of data from the most variable hay lot suggested that forage quality of any lot of 400-kg alfalfa hay bales should be adequately represented by 12 bales sampled once per bale.
Subsonic Round and Rectangular Twin Jet Flow Effects
NASA Technical Reports Server (NTRS)
Bozak, Rick; Wernet, Mark
2014-01-01
Subsonic and supersonic aircraft concepts proposed by NASAs Fundamental Aeronautics Program have integrated propulsion systems with asymmetric nozzles. The asymmetry in the exhaust of these propulsion systems creates asymmetric flow and acoustic fields. The flow asymmetries investigated in the current study are from two parallel round, 2:1, and 8:1 aspect ratio rectangular jets at the same nozzle conditions. The flow field was measured with streamwise and cross-stream particle image velocimetry (PIV). A large dataset of single and twin jet flow field measurements was acquired at subsonic jet conditions. The effects of twin jet spacing and forward flight were investigated. For round, 2:1, and 8:1 rectangular twin jets at their closest spacings, turbulence levels between the two jets decreased due to enhanced jet mixing at near static conditions. When the flight Mach number was increased to 0.25, the flow around the twin jet model created a velocity deficit between the two nozzles. This velocity deficit diminished the effect of forward flight causing an increase in turbulent kinetic energy relative to a single jet. Both of these twin jet flow field effects decreased with increasing twin jet spacing relative to a single jet. These variations in turbulent kinetic energy correlate with changes in far-field sound pressure level.
Logically rectangular mixed methods for Darcy flow on general geometry
Arbogast, T.; Keenan, P.T.; Wheeler, M.F.; Yotov, I.
1995-12-31
The authors consider an expanded mixed finite element formulation (cell centered finite difference) for Darcy flow with a tensor absolute permeability. The reservoir can be geometrically general with internal features, but the computational domain is rectangular. The method is defined on a curvilinear grid that need not be orthogonal, obtained by mapping the rectangular, computational grid. The original flow problem becomes a similar problem with a modified permeability on the computational grid. Quadrature rules turn the mixed method into a cell-centered finite difference method with a 9 point stencil in 2-D and 19 in 3-D. As shown by theory and experiment, if the modified permeability on the computational domain is smooth, then the convergence rate is optimal and both pressure and velocity are superconvergent at certain points. If not, Lagrange multiplier pressures can be introduced on boundaries of elements so that optimal convergence is retained. This modification presents only small changes in the solution process; in fact, the same parallel domain decomposition algorithms can be applied with little or no change to the code if the modified permeability is smooth over the subdomains. This Lagrange multiplier procedure can be used to extend the difference scheme to multi-block domains, and to give a coupling with unstructured grids. In all cases, the mixed formulation is locally conservative. Computational results illustrate the advantage and convergence of this method.
Richards Equation Solver; Rectangular Finite Volume Flux Updating Solution.
2002-01-18
Version: 00 POLYRES solves the transient, two-dimensional, Richards equation for water flow in unsaturated-saturated soils. The package is specifically designed to allow the user to easily model complex polygon-shaped regions. Flux, head, and unit gradient boundary conditions can be used. Spatial variation of the hydraulic properties can be defined across individual polygon-shaped subdomains, called objects. These objects combine to form a polygon-shaped model domain. Each object can have its own distribution of hydraulic parameters. Themore » resulting model domain and polygon-shaped internal objects are mapped onto a rectangular, finite-volume, computational grid by a preprocessor. This allows the user to specify model geometry independently of the underlying grid and greatly simplifies user input for complex geometries. In addition, this approach significantly reduces the computational requirements since complex geometries are actually modeled on a rectangular grid. This results in well-structured, finite difference-like systems of equations that require minimal storage and are very efficient to solve.« less
Efficient and accurate sound propagation using adaptive rectangular decomposition.
Raghuvanshi, Nikunj; Narain, Rahul; Lin, Ming C
2009-01-01
Accurate sound rendering can add significant realism to complement visual display in interactive applications, as well as facilitate acoustic predictions for many engineering applications, like accurate acoustic analysis for architectural design. Numerical simulation can provide this realism most naturally by modeling the underlying physics of wave propagation. However, wave simulation has traditionally posed a tough computational challenge. In this paper, we present a technique which relies on an adaptive rectangular decomposition of 3D scenes to enable efficient and accurate simulation of sound propagation in complex virtual environments. It exploits the known analytical solution of the Wave Equation in rectangular domains, and utilizes an efficient implementation of the Discrete Cosine Transform on Graphics Processors (GPU) to achieve at least a 100-fold performance gain compared to a standard Finite-Difference Time-Domain (FDTD) implementation with comparable accuracy, while also being 10-fold more memory efficient. Consequently, we are able to perform accurate numerical acoustic simulation on large, complex scenes in the kilohertz range. To the best of our knowledge, it was not previously possible to perform such simulations on a desktop computer. Our work thus enables acoustic analysis on large scenes and auditory display for complex virtual environments on commodity hardware. PMID:19590105
Measurement strategy for rectangular electrical capacitance tomography sensor
Ye, Jiamin; Ge, Ruihuan; Qiu, Guizhi; Wang, Haigang
2014-04-11
To investigate the influence of the measurement strategy for the rectangular electrical capacitance tomography (ECT) sensor, a Finite Element Method (FEM) is utilized to create the model for simulation. The simulation was carried out using COMSOL Multiphysics(trade mark, serif) and Matlab(trade mark, serif). The length-width ratio of the rectangular sensing area is 5. Twelve electrodes are evenly arranged surrounding the pipe. The covering ratio of the electrodes is 90%. The capacitances between different electrode pairs are calculated for a bar distribution. The air of the relative permittivity 1.0 and the material of the permittivity 3.0 are used for the calibration. The relative permittivity of the second phase is 3.0. The noise free and noise data are used for the image reconstruction using the Linear Back Projection (LBP). The measurement strategies with 1-, 2- and 4- electrode excitation are compared using the correlation coefficient. Preliminary results show that the measurement strategy with 2-electrode excitation outperforms other measurement strategies with 1- or 4-electrode excitation.
Rectangular capture area to circular combustor scramjet engine
NASA Technical Reports Server (NTRS)
Pinckney, S. Z.
1978-01-01
A new concept for a scramjet engine design was presented. The inlet transformed a rectangular shaped capture stream into a cross section which was almost circular in shape at the inlet throat or combustor entrance. The inlet inner surface was designed by the method of streamline tracing. The high pressure and temperature regions of the combustor were almost circular in shape and thus the benefits of hoop stresses in relation to structural weight could be utilized to reduce combustor and engine weights. The engine had a center body consisting of a 20 deg included angle cone, followed by a constant diameter cylinder. Fuel injection struts were arranged in a radial array and were swept 54 deg from the center body to the inlet inner surface and had values of length to maximum average thickness between 5.6and 6.6 which were felt to be structurally reasonable. Combustor wetted areas were shown to be less than those of the present fully rectangular engine concept.
Phase space analysis of multipactor saturation in rectangular waveguide
NASA Astrophysics Data System (ADS)
Lingwood, C. J.; Burt, G.; Dexter, A. C.; Smith, J. D. A.; Goudket, P.; Stoltz, P. H.
2012-03-01
In certain high power RF systems multipactor cannot be avoided for all operating points, but its existence places limits on performance, efficiency, lifetime, and reliability. As an example multipactor in the input couplers of superconducting RF cavities can be a major limitation to the maximum RF power. Several studies have concentrated on rectangular waveguide input couplers which are used in many light sources. Most of these studies neglect space charge assuming that the effect of space charge is simply to defocus the electron bunches. Modelling multipactor to saturation is of interest in determining the performance of waveguide under a range of conditions. Particle-in-cell modelling including space charge has been performed for 500 MHz half-height rectangular waveguide. Phase plots of electron trajectories can aid understanding the processes taking place in the multipactor. Results strongly suggest that the multipacting trajectories are strongly perturbed by space charge causing the electrons to transition from two-surface to single-surface trajectories as the multipactor approaches saturation.
Versatile patterns of multiple rectangular noise-like pulses in a fiber laser.
Huang, Yu-Qi; Qi, You-Li; Luo, Zhi-Chao; Luo, Ai-Ping; Xu, Wen-Cheng
2016-04-01
We report on the generation of versatile patterns of multiple rectangular noise-like pulses (NLPs) in a fiber laser mode-locked by nonlinear amplifying loop mirror (NALM). Benefiting from the strengthened nonlinear effect of a segment of highly nonlinear fiber (HNLF) in the loop, multiple rectangular NLPs with various patterns are formed depending on the cavity parameter settings. In particular, the multiple rectangular NLPs could possess unequal packet durations, which is different from the conventional multi-soliton patterns. The experimental results contribute to further understanding the characteristics of the rectangular NLP and the dynamics of multi-pulse patterns. PMID:27137025
Round versus rectangular: Does the plot shape matter?
NASA Astrophysics Data System (ADS)
Iserloh, Thomas; Bäthke, Lars; Ries, Johannes B.
2016-04-01
Field rainfall simulators are designed to study soil erosion processes and provide urgently needed data for various geomorphological, hydrological and pedological issues. Due to the different conditions and technologies applied, there are several methodological aspects under review of the scientific community, particularly concerning design, procedures and conditions of measurement for infiltration, runoff and soil erosion. Extensive discussions at the Rainfall Simulator Workshop 2011 in Trier and the Splinter Meeting at EGU 2013 "Rainfall simulation: Big steps forward!" lead to the opinion that the rectangular shape is the more suitable plot shape compared to the round plot. A horizontally edging Gerlach trough is installed for sample collection without forming unnatural necks as is found at round or triangle plots. Since most research groups did and currently do work with round plots at the point scale (<1m²), a precise analysis of the differences between the output of round and square plots are necessary. Our hypotheses are: - Round plot shapes disturb surface runoff, unnatural fluvial dynamics for the given plot size such as pool development especially directly at the plot's outlet occur. - A square plot shape prevent these problems. A first comparison between round and rectangular plots (Iserloh et al., 2015) indicates that the rectangular plot could indeed be the more suitable, but the rather ambiguous results make a more elaborate test setup necessary. The laboratory test setup includes the two plot shapes (round, square), a standardised silty substrate and three inclinations (2°, 6°, 12°). The analysis of the laboratory test provide results on the best performance concerning undisturbed surface runoff and soil/water sampling at the plot's outlet. The analysis of the plot shape concerning its influence on runoff and erosion shows that clear methodological standards are necessary in order to make rainfall simulation experiments comparable. Reference
Plastic buckling of a rectangular plate under edge thrusts
NASA Technical Reports Server (NTRS)
Handelman, G H; Prager, W
1949-01-01
The fundamental equations for the plastic buckling of a rectangular plate under edge thrusts are developed on the basis of a new set of stress-strain relations for the behavior of a metal in the plastic range. These relations are derived for buckling from a state of uniform compression. The fundamental equation for the buckling of a simply compressed plate together with typical boundary conditions is then developed and the results are applied to calculating the buckling loads of a thin strip, a simply supported plate, and a cruciform section. Comparisons with the theories of Timoshenko and Ilyushin are made. Finally, an energy method is given which can be used for finding approximate values of the critical load.
Impedance of curved rectangular spiral coils around a conductive cylinder
NASA Astrophysics Data System (ADS)
Burke, S. K.; Ditchburn, R. J.; Theodoulidis, T. P.
2008-07-01
Eddy-current induction due to a thin conformable coil wrapped around a long conductive cylinder is examined using a second-order vector potential formalism. Compact closed-form expressions are derived for the self- and mutual impedances of curved rectangular spiral coils (i) in free space and (ii) when wrapped around the surface of the cylindrical rod. The validity of these expressions was tested against the results of a systematic series of experiments using a cylindrical Al-alloy rod and conformable coils manufactured using flexible printed-circuit-board technology. The theoretical expressions were in very good agreement with the experimental measurements. The significance of the results for eddy-current nondestructive inspection using flexible coils and flexible coil arrays is discussed.
Vibrations of cantilevered shallow cylindrical shells of rectangular planform
NASA Technical Reports Server (NTRS)
Leissa, A. W.; Lee, J. K.; Wang, A. J.
1981-01-01
A cantilevered, shallow shell of circular cylindrical curvature and rectangular planform exhibits free vibration behavior which differs considerably from that of a cantilevered beam or of a flat plate. Some numerical results can be found for the problem in the previously published literature, mainly obtained by using various finite element methods. The present paper is the first definitive study of the problem, presenting accurate non-dimensional frequency parameters for wide ranges of aspect ratio, shallowness ratio and thickness ratio. The analysis is based upon shallow shell theory. Numerical results are obtained by using the Ritz method, with algebraic polynomial trial functions for the displacements. Convergence is investigated, with attention being given both to the number of terms taken for each co-ordinate direction and for each of the three components of displacement. Accuracy of the results is also established by comparison with finite element results for shallow shells and with other accurate flat plate solutions.
Thermoelectric effects in a rectangular Aharonov-Bohm geometry
NASA Astrophysics Data System (ADS)
Pye, A. J.; Faux, D. A.; Kearney, M. J.
2016-04-01
The thermoelectric transport properties of a rectangular Aharonov-Bohm ring at low temperature are investigated using a theoretical approach based on Green's functions. The oscillations in the transmission coefficient as the field is varied can be used to tune the thermoelectric response of the ring. Large magnitude thermopowers are obtainable which, in conjunction with low conductance, can result in a high thermoelectric figure of merit. The effects of single site impurities and more general Anderson disorder are considered explicitly in the context of evaluating their effect on the Fano-type resonances in the transmission coefficient. Importantly, it is shown that even for moderate levels of disorder, the thermoelectric figure of merit can remain significant, increasing the appeal of such structures from the perspective of specialist thermoelectric applications.
Oscillating laminar electrokinetic flow in infinitely extended rectangular microchannels.
Yang, J; Bhattacharyya, A; Masliyah, J H; Kwok, D Y
2003-05-01
This paper has addressed analytically the problem of laminar flow in microchannels with rectangular cross-section subjected to a time-dependent sinusoidal pressure gradient and a sinusoidal electric field. The analytical solution has been determined based on the Debye-Hückel approximation of a low surface potential at the channel wall. We have demonstrated that Onsager's principle of reciprocity is valid for this problem. Parametric studies of streaming potential have shown the dependence of the electroviscous effect not only on the Debye length, but also on the oscillation frequency and the microchannel width. Parametric studies of electroosmosis demonstrate that the flow rate decreases due to an increase in frequency. The obtained solutions for both the streaming potential and electroosmotic flows become those for flow between two parallel plates in the limit of a large aspect ratio. PMID:12725820
Vibrations of cantilevered shallow cylindrical shells of rectangular planform
NASA Astrophysics Data System (ADS)
Leissa, A. W.; Lee, J. K.; Wang, A. J.
1981-10-01
A cantilevered, shallow shell of circular cylindrical curvature and rectangular planform exhibits free vibration behavior which differs considerably from that of a cantilevered beam or of a flat plate. Some numerical results can be found for the problem in the previously published literature, mainly obtained by using various finite element methods. The present paper is the first definitive study of the problem, presenting accurate non-dimensional frequency parameters for wide ranges of aspect ratio, shallowness ratio and thickness ratio. The analysis is based upon shallow shell theory. Numerical results are obtained by using the Ritz method, with algebraic polynomial trial functions for the displacements. Convergence is investigated, with attention being given both to the number of terms taken for each co-ordinate direction and for each of the three components of displacement. Accuracy of the results is also established by comparison with finite element results for shallow shells and with other accurate flat plate solutions.
Screech Tones of Supersonic Jets from Bevelled Rectangular Nozzles
NASA Technical Reports Server (NTRS)
Tam, Christopher K. W.; Shen, Hao; Raman, Ganesh
1997-01-01
It is known experimentally that an imperfectly expanded rectangular jet from a thin-lip convergent nozzle emits only a single dominant screech tone. The frequency of the screech tone decreases continuously with increase in jet Mach number. However, for a supersonic jet issued from a bevelled nozzle or a convergent-divergent nozzle with straight side walls, the shock cell structure and the screech frequency pattern are fairly complicated and have not been predicted before. In this paper, it is shown that the shock cell structures of these jets can be decomposed into waveguide modes of the jet flow. The screech frequencies are related to the higher-order waveguide modes following the weakest-link screech tone theory. The measured screech frequencies are found to compare well with the predicted screech frequency curves.
Lidar profiling by long rectangular-like chopped laser pulses
NASA Astrophysics Data System (ADS)
Stoyanov, Dimitar V.; Gurdev, Ljuan L.; Kolarov, Georgi; Vankov, O. I.
2000-06-01
A novel, simple method is developed and tested (experimentally and by simulations) for effective, high- resolution retrieving of time-resolved lidar profiles for long rectangular-like laser pulses with arbitrary shapes of their leading and trailing edges. Such pulses are typically created by chopping cw optical radiation. The processing algorithm is based on differentiation and iteration procedures and avoids the use of divisions or deconvolutions that are often responsible for some errors and increases in the noise. Comparisons with pulsed and pseudo-random noise modulation lidar methods are given. The method enables a simplification of the entire lidar hardware. No powerful pulsed supplies, high driving pulsed voltages, complicated optical modulations, etc. are required. It could be very attractive for high-resolution, wide-spectral-band lidar measurements in the atmosphere, ocean, etc., using arbitrary optical emitters, especially for closer distances.
Rectangular Waveguides with Two Conventional and Two Superconducting Walls
NASA Technical Reports Server (NTRS)
Yalamanchili, Raj; Qiu, Zheng An; Wang, Yen-Chu
1995-01-01
The propagation properties of transverse electric TE(sup pm) modes and their dispersion relations in rectangular waveguides with two conventional and two superconducting walls, derived by using the Meissner boundary conditions on the superconducting walls, are presented. In addition to recovering some previously known results, some novel results have been obtained: the cut-off wavelength of the dominant TE(sup 10) mode is greater than that of the conventional TE(sub 10) mode, and the tangential electric field and normal magnetic field for the dominant mode TE(sup 10) exist on the superconducting surfaces. Expressions for electromagnetic components, surface currents, attenuation coefficient, maximum transmitted power, dispersion and wave impedance are also presented.
Some features of tones generated by an underexpanded rectangular jet
NASA Astrophysics Data System (ADS)
Krothapalli, A.; Baganoff, D.; Karamcheti, K.; Hsia, Y.
1981-01-01
An experimental investigation has been carried out on an underexpanded jet of air issuing from a convergent rectangular nozzle. Schlieren pictures of the flow field along with microphone and hot wire measurements in the near field of the jet were obtained at different pressure ratios. At the pressure ratio for maximum screech sound radiation, the schlieren photographs show a very strong organized cylindrical wave pattern on either side of the jet with their source being located at the end of the third shock cell. Associated with this wave pattern is a large angle of spread of the jet of about 36 degrees. Experiments using a reflecting surface near the nozzle exit show that the flow can be either destabilized or stabilized by a small rigid plate located only on one side, and in almost all positions.
Oscillating flow and separation of species in rectangular channels
NASA Astrophysics Data System (ADS)
Hacioglu, A.; Narayanan, R.
2016-07-01
The mass transfer and separation of species in a tube using oscillatory flows are strongly affected by the fluid flow profiles in the tube. It has been well established that oscillatory motion in a one-dimensional flow configuration leads to a single tuning dimensionless frequency, where optimum separation may be effected. In this work, the effect on species separation by two-dimensional laminar flow arising in a rectangular cross section is studied and a surprising result is that a second tuning frequency may occur at lower dimensionless oscillation frequencies. The physics reveals that this new optimum disappears when the aspect ratio is either very large or close to unity. These observations are related to the flow profiles at different aspect ratios.
Geometrically nonlinear vibrations of rectangular plates carrying a concentrated mass
NASA Astrophysics Data System (ADS)
Amabili, M.
2010-10-01
Nonlinear forced vibrations of rectangular plates carrying a central concentrated mass are studied. The plate is assumed to have immovable edges and rotational springs; numerical results are presented for clamped plates. The Von Kármán nonlinear plate theory is used, but in-plane inertia in both the plate and the mass is retrained. The problem is discretized into a multi-degree-of-freedom (dof) system by using an energy approach and Lagrange equations taking damping into account. A pseudo-arclength continuation method is used in order to obtain numerical solutions. Results are presented as both (i) frequency-amplitude curves and (ii) time domain responses. The effect of gravity and the effect of the consequent initial plate deflection are also investigated.
Flow-Field Surveys for Rectangular Nozzles. Supplement
NASA Technical Reports Server (NTRS)
Zaman, K. B. M. Q.
2012-01-01
Flow field survey results for three rectangular nozzles are presented for a low subsonic condition obtained primarily by hot-wire anemometry. The three nozzles have aspect ratios of 2:1, 4:1 and 8:1. A fourth case included has 2:1 aspect ratio with chevrons added to the long edges. Data on mean velocity, turbulent normal and shear stresses as well as streamwise vorticity are presented covering a streamwise distance up to sixteen equivalent diameters from the nozzle exit. These detailed flow properties, including initial boundary layer characteristics, are usually difficult to measure in high speed flows and the primary objective of the study is to aid ongoing and future computational and noise modeling efforts. This supplement contains data files, charts and source code.
Numerical Simulation of Turbulent Jets with Rectangular Cross-Section
NASA Technical Reports Server (NTRS)
Wilson, Robert V.; Demuren, Ayodeji O.
1997-01-01
Three-dimensional turbulent jets with rectangular cross-section are simulated with a finite-difference numerical method. The full Navier-Stokes equations are solved at low Reynolds numbers, whereas at the high Reynolds numbers filtered forms of the equations are solved along with a sub-grid scale model to approximate effects of the unresolved scales. A 2-N storage, third-order Runge-Kutta scheme is used for temporal discretization and a fourth-order compact scheme is used for spatial discretization. Computations are performed for different inlet conditions which represent different types of jet forcing. The phenomenon of axis-switching is observed, and it is confirmed that this is based on self-induction of the vorticity field. Budgets of the mean streamwise velocity show that convection is balanced by gradients of the Reynolds stresses and the pressure.
Elastostatic stress analysis of orthotropic rectangular center-cracked plates
NASA Technical Reports Server (NTRS)
Gyekenyesi, G. S.; Mendelson, A.
1972-01-01
A mapping-collocation method was developed for the elastostatic stress analysis of finite, anisotropic plates with centrally located traction-free cracks. The method essentially consists of mapping the crack into the unit circle and satisfying the crack boundary conditions exactly with the help of Muskhelishvili's function extension concept. The conditions on the outer boundary are satisfied approximately by applying the method of least-squares boundary collocation. A parametric study of finite-plate stress intensity factors, employing this mapping-collocation method, is presented. It shows the effects of varying material properties, orientation angle, and crack-length-to-plate-width and plate-height-to-plate-width ratios for rectangular orthotropic plates under constant tensile and shear loads.
Flow field induced particle accumulation inside droplets in rectangular channels.
Hein, Michael; Moskopp, Michael; Seemann, Ralf
2015-07-01
Particle concentration is a basic operation needed to perform washing steps or to improve subsequent analysis in many (bio)-chemical assays. In this article we present field free, hydrodynamic accumulation of particles and cells in droplets flowing within rectangular micro-channels. Depending on droplet velocity, particles either accumulate at the rear of the droplet or are dispersed over the entire droplet cross-section. We show that the observed particle accumulation behavior can be understood by a coupling of particle sedimentation to the internal flow field of the droplet. The changing accumulation patterns are explained by a qualitative change of the internal flow field. The topological change of the internal flow field, however, is explained by the evolution of the droplet shape with increasing droplet velocity altering the friction with the channel walls. In addition, we demonstrate that accumulated particles can be concentrated, removing excess dispersed phase by splitting the droplet at a simple channel junction. PMID:26032835
Aerodynamic characteristics of bodies with rectangular cross section
NASA Astrophysics Data System (ADS)
Knoche, H. G.; Schamel, W.; Esch, H.; Schneider, W.
Systematic wind tunnel tests for a series of missile bodies were conducted by varying cross section shape and body length in the subsonic Mach number range and up to high angles of attack. Tests with a body-wing and a body-tail configuration were performed in order to investigate the body-wing and body-tail interference for bodies of revolution and bodies with rectangular cross section. At a constant angle of attack, the boxlike body supplies far more normal force than the body of revolution with the same cross section area. The boxlike body shows strong coupling effects between the pitch, yaw and roll. The interference effect of the wing and body can be described well, in the case of boxlike bodies with wings in high or low wing positions, by the known slender body interference factors, assuming the width of the box to be the diameter of an equivalent, axially symetrical body.
Finite-element analysis of corner cracks in rectangular bars
NASA Technical Reports Server (NTRS)
Raju, L. S.; Newman, J. C., Jr.
1987-01-01
Stress intensity factors for a wide range of quarter-elliptical corner cracks in rectangular bars are presented. Cracked configurations were subjected to remote tension, in-plane bending, or out-of-plane bending. Results were compared with other numerical results for a quarter-circular corner crack configuration. The present results along the interior of the crack generally agreed within 3 percent with those from the literature. Some larger differences (3 to 13 percent) were observed near the intersection of the crack front and the free surfaces in the boundary layer region. Analyses were performed to study the effect of mesh refinement in the boundary layer region and the influence of Poisson's ratio on the distribution of stress-intensity factors.
Performance analysis of SOI MOSFET with rectangular recessed channel
NASA Astrophysics Data System (ADS)
Singh, M.; Mishra, S.; Mohanty, S. S.; Mishra, G. P.
2016-03-01
In this paper a two dimensional (2D) rectangular recessed channel-silicon on insulator metal oxide semiconductor field effect transistor (RRC-SOI MOSFET), using the concept of groove between source and drain regions, which is one of the channel engineering technique to suppress the short channel effect (SCE). This suppression is mainly due to corner potential barrier of the groove and the simulation is carried out by using ATLAS 2D device simulator. To have further improvement of SCE in RRC-SOI MOSFET, three more devices are designed by using dual material gate (DMG) and gate dielectric technique, which results in formation of devices i.e. DMRRC-SOI,MLSMRRC-SOI, MLDMRRC-SOI MOSFET. The effect of different structures of RRC-SOI on AC and RF parameters are investigated and the importance of these devices over RRC MOSFET regarding short channel effect is analyzed.
Quantitative study of rectangular waveguide behavior in the THz.
Rowen, Adam M.; Nordquist, Christopher Daniel; Wanke, Michael Clement
2009-10-01
This report describes our efforts to quantify the behavior of micro-fabricated THz rectangular waveguides on a configurable, robust semiconductor-based platform. These waveguides are an enabling technology for coupling THz radiation directly from or to lasers, mixers, detectors, antennas, and other devices. Traditional waveguides fabricated on semiconductor platforms such as dielectric guides in the infrared or co-planar waveguides in the microwave regions, suffer high absorption and radiative losses in the THz. The former leads to very short propagation lengths, while the latter will lead to unwanted radiation modes and/or crosstalk in integrated devices. This project exploited the initial developments of THz micro-machined rectangular waveguides developed under the THz Grand Challenge Program, but instead of focusing on THz transceiver integration, this project focused on exploring the propagation loss and far-field radiation patterns of the waveguides. During the 9 month duration of this project we were able to reproduce the waveguide loss per unit of length in the waveguides and started to explore how the loss depended on wavelength. We also explored the far-field beam patterns emitted by H-plane horn antennas attached to the waveguides. In the process we learned that the method of measuring the beam patterns has a significant impact on what is actually measured, and this may have an effect on most of the beam patterns of THz that have been reported to date. The beam pattern measurements improved significantly throughout the project, but more refinements of the measurement are required before a definitive determination of the beam-pattern can be made.
Underexpanded Screeching Jets From Circular, Rectangular, and Elliptic Nozzles
NASA Technical Reports Server (NTRS)
Panda, J.; Raman, G.; Zaman, K. B. M. Q.
2004-01-01
The screech frequency and amplitude, the shock spacing, the hydrodynamic-acoustic standing wave spacing, and the convective velocity of large organized structures are measured in the nominal Mach number range of 1.1 less than or = Mj less that or = l0.9 for supersonic, underexpanded jets exhausting from a circular, a rectangular and an elliptic nozzle. This provides a carefully measured data set useful in comparing the importance of various physical parameters in the screech generation process. The hydrodynamic-acoustic standing wave is formed between the potential pressure field of large turbulent structures and the acoustic pressure field of the screech sound. It has been demonstrated earlier that in the currently available screech frequency prediction models replacement of the shock spacing by the standing wave spacing provides an exact expression. In view of this newly found evidence, a comparison is made between the average standing wavelength and the average shock spacing. It is found that there exists a small, yet important, difference, which is dependent on the azimuthal screech mode. For example, in the flapping modes of circular, rectangular, and elliptic jets, the standing wavelength is slightly longer than the shock spacing, while for the helical screech mode in a circular jet the opposite is true. This difference accounts for the departure of the existing models from predicting the exact screech frequency. Another important parameter, necessary in screech prediction, is the convective velocity of the large organized structures. It is demonstrated that the presence of the hydrodynamic-acoustic standing wave, even inside the jet shear layer, becomes a significant source of error in the convective velocity data obtained using the conventional methods. However, a new relationship, using the standing wavelength and screech frequency is shown to provide more accurate results.
Rectangular Dielectric-loaded Structures for Achieving High Acceleration Gradients
Wang Changbiao; Yakovlev, V. P.; Marshall, T. C.; LaPointe, M. A.; Hirshfield, J. L.
2006-11-27
Rectangular dielectric-loaded structures are described that may sustain higher acceleration gradients than conventional all-metal structures with similar apertures. One structure is a test cavity designed to ascertain the breakdown limits of dielectrics, while a second structure could be the basis for a two-beam accelerator. CVD diamond is an attractive dielectric for a high-gradient structure, since the published DC breakdown limit for CVD diamond is {approx} 2 GV/m, although the limit has never been determined for RF fields. Here we present a design of a diamond-lined test cavity to measure the breakdown limit. The designed cavity operates at 34 GHz, where with 10-MW input power it is expected to produce an {approx}800 MV/m field on the diamond surface - provided breakdown is avoided. The two channel rectangular dielectric-loaded waveguide could be a two-beam accelerator structure, in which a drive beam is in one channel and an accelerated beam is in the other. The RF power produced by drive bunches in the drive channel is continuously coupled to the acceleration channel. The ratio of fields in the channels (transformer ratio) for the operating mode can be designed by adjusting the dimensions of the structure. An example of the two-channel structure is described, in which a train of five 3-nC drive bunches excites wake fields in the accelerator channel of up to 1.3 GV/m with a transformer ratio of 10 for the design mode.
An approximate algorithm for the flux from a rectangular volume source
Wallace, O.J.
1994-11-09
An exact semi-analytic formula for the flux from a rectangular surface source with a slab shield has been derived and the required function table has been calculated. This formula is the basis for an algorithm which gives a good approximation for the flux from a rectangular volume source. No other hand calculation method for this source geometry is available in the literature.
Finite element fatigue analysis of rectangular clutch spring of automatic slack adjuster
NASA Astrophysics Data System (ADS)
Xu, Chen-jie; Luo, Zai; Hu, Xiao-feng; Jiang, Wen-song
2015-02-01
The failure of rectangular clutch spring of automatic slack adjuster directly affects the work of automatic slack adjuster. We establish the structural mechanics model of automatic slack adjuster rectangular clutch spring based on its working principle and mechanical structure. In addition, we upload such structural mechanics model to ANSYS Workbench FEA system to predict the fatigue life of rectangular clutch spring. FEA results show that the fatigue life of rectangular clutch spring is 2.0403×105 cycle under the effect of braking loads. In the meantime, fatigue tests of 20 automatic slack adjusters are carried out on the fatigue test bench to verify the conclusion of the structural mechanics model. The experimental results show that the mean fatigue life of rectangular clutch spring is 1.9101×105, which meets the results based on the finite element analysis using ANSYS Workbench FEA system.
Test Cases for a Rectangular Supercritical Wing Undergoing Pitching Oscillations
NASA Technical Reports Server (NTRS)
Bennett, Robert M.
2000-01-01
Steady and unsteady measured pressures for a Rectangular Supercritical Wing (RSW) undergoing pitching oscillations have been presented. From the several hundred compiled data points, 27 static and 36 pitching oscillation cases have been proposed for computational Test Cases to illustrate the trends with Mach number, reduced frequency, and angle of attack. The wing was designed to be a simple configuration for Computational Fluid Dynamics (CFD) comparisons. The wing had an unswept rectangular planform plus a tip of revolution, a panel aspect ratio of 2.0, a twelve per cent thick supercritical airfoil section, and no twist. The model was tested over a wide range of Mach numbers, from 0.27 to 0.90, corresponding to low subsonic flows up to strong transonic flows. The higher Mach numbers are well beyond the design Mach number such as might be required for flutter verification beyond cruise conditions. The pitching oscillations covered a broad range of reduced frequencies. Some early calculations for this wing are given for lifting pressure as calculated from a linear lifting surface program and from a transonic small perturbation program. The unsteady results were given primarily for a mild transonic condition at M = 0.70. For these cases the agreement with the data was only fair, possibly resulting from the omission of viscous effects. Supercritical airfoil sections are known to be sensitive to viscous effects (for example, one case cited). Calculations using a higher level code with the full potential equations have been presented for one of the same cases, and with the Euler equations. The agreement around the leading edge was improved, but overall the agreement was not completely satisfactory. Typically for low-aspect-ratio rectangular wings, transonic shock waves on the wing tend to sweep forward from root to tip such that there are strong three-dimensional effects. It might also be noted that for most of the test, the model was tested with free transition, but a
NASA Astrophysics Data System (ADS)
Crowgey, Benjamin Reid
Rectangular waveguide methods are appealing for measuring isotropic and anisotropic materials because of high signal strength due to field confinement, and the ability to control the polarization of the applied electric field. As a stepping stone to developing methods for characterizing materials with fully-populated anisotropic tensor characteristics, techniques are presented in this dissertation to characterize isotropic, biaxially anisotropic, and gyromagnetic materials. Two characterization techniques are investigated for each material, and thus six different techniques are described. Additionally, a waveguide standard is introduced which may be used to validate the measurement of the permittivity and permeability of materials at microwave frequencies. The first characterization method examined is the Nicolson-Ross-Weir (NRW) technique for the extraction of isotropic parameters of a sample completely filling the cross-section of a rectangular waveguide. A second technique is proposed for the characterization of an isotropic conductor-backed sample filling the cross-section of a waveguide. If the sample is conductor-backed, and occupies the entire cross-section, a transmission measurement is not available, and thus a method must be found for providing two sufficiently different reflection measurements.The technique proposed here is to place a waveguide iris in front of the sample, exposing the sample to a spectrum of evanescent modes. By measuring the reflection coefficient with and without an iris, the necessary two data may be obtained to determine the material parameters. A mode-matching approach is used to determine the theoretical response of a sample placed behind the waveguide iris. This response is used in a root-searching algorithm to determine permittivity and permeability by comparing to measurements of the reflection coefficient. For the characterization of biaxially anisotropic materials, the first method considers an extension of the NRW technique
TFSSRA - THICK FREQUENCY SELECTIVE SURFACE WITH RECTANGULAR APERTURES
NASA Technical Reports Server (NTRS)
Chen, J. C.
1994-01-01
Thick Frequency Selective Surface with Rectangular Apertures (TFSSRA) was developed to calculate the scattering parameters for a thick frequency selective surface with rectangular apertures on a skew grid at oblique angle of incidence. The method of moments is used to transform the integral equation into a matrix equation suitable for evaluation on a digital computer. TFSSRA predicts the reflection and transmission characteristics of a thick frequency selective surface for both TE and TM orthogonal linearly polarized plane waves. A model of a half-space infinite array is used in the analysis. A complete set of basis functions with unknown coefficients is developed for the waveguide region (waveguide modes) and for the free space region (Floquet modes) in order to represent the electromagnetic fields. To ensure the convergence of the solutions, the number of waveguide modes is adjustable. The method of moments is used to compute the unknown mode coefficients. Then, the scattering matrix of the half-space infinite array is calculated. Next, the reference plane of the scattering matrix is moved half a plate thickness in the negative z-direction, and a frequency selective surface of finite thickness is synthesized by positioning two plates of half-thickness back-to-back. The total scattering matrix is obtained by cascading the scattering matrices of the two half-space infinite arrays. TFSSRA is written in FORTRAN 77 with single precision. It has been successfully implemented on a Sun4 series computer running SunOS, an IBM PC compatible running MS-DOS, and a CRAY series computer running UNICOS, and should run on other systems with slight modifications. Double precision is recommended for running on a PC if many modes are used or if high accuracy is required. This package requires the LINPACK math library, which is included. TFSSRA requires 1Mb of RAM for execution. The standard distribution medium for this program is one 5.25 inch 360K MS-DOS format diskette. It is also
Constructal design for a rectangular body with nonuniform heat generation
NASA Astrophysics Data System (ADS)
Feng, Huijun; Chen, Lingen; Xie, Zhihui; Sun, Fengrui
2016-08-01
Nonuniform heat generation models with constant and variable cross-section high-conductivity channels (HCCs) are built in this paper. The minimum dimensionless peak temperature (DPT) is taken as the optimization objective. Different from the models with uniform heat generation and constant cross-section HCCs built by Bejan (1997) and Ledezma et al. (1997), the model with nonuniform heat generation and variable cross-section HCC is more practical and can help to improve the heat conduction performance of a thermal system. The results show that for the rectangular first-order assembly (RFOA) with nonuniform heat generation, there exist both the optimal shape of the RFOA and the optimal HCCs width ratio, which lead to the minimum DPT. They are different from those with uniform heat generation. When the heat is nonuniformly generated in the RFOA, the minimum DPT of the RFOA with variable cross-section HCC is reduced by 12.11% compared with that with constant cross-section HCC. Moreover, the numerical results are also verified by the analytical method.
Streamwise Vortex Formation Upstream of a Rectangular Nozzle
NASA Astrophysics Data System (ADS)
Hsu, T. Y.; Wei, T.
2001-11-01
High resolution DPIV measurements were made to examine the hydrodynamic stability of initially laminar flow passing through a sudden contraction. This motivation for this study was understanding the effects of nozzle geometry and turbulence on papermaking. Experiments were conducted with water using a simplified two-dimensional rectangular nozzle constructed to match the Reynolds number of industrial papermaking machines. The nozzle consisted of a 60 cm wide x 10 cm high channel whose downstream end could be blocked by as much as 50orthogonal planes at various positions upstream of the nozzle exit. The Reynolds number range, based on the jet height and the free stream velocity (1-2 m/s), was 10,000 to 100,000. An unsteady spanwise vortex 1.6 cm in diameter was found at the corner of the vertical solid wall and the top wall of the contraction. Further, unsteady streamwise vortices with 2 cm in diameter were identified both visually and by using spectrum analysis. These findings will be related to the streaks found in a sheet of paper.
Generation of Higher Order Modes in a Rectangular Duct
NASA Technical Reports Server (NTRS)
Gerhold, Carl H.; Cabell, Randolph H.; Brown, Donald E.
2004-01-01
Advanced noise control methodologies to reduce sound emission from aircraft engines take advantage of the modal structure of the noise in the duct. This noise is caused by the interaction of rotor wakes with downstream obstructions such as exit guide vanes. Mode synthesis has been accomplished in circular ducts and current active noise control work has made use of this capability to cancel fan noise. The goal of the current effort is to examine the fundamental process of higher order mode propagation through an acoustically treated, curved duct. The duct cross-section is rectangular to permit greater flexibility in representation of a range of duct curvatures. The work presented is the development of a feedforward control system to generate a user-specified modal pattern in the duct. The multiple-error, filtered-x LMS algorithm is used to determine the magnitude and phase of signal input to the loudspeakers to produce a desired modal pattern at a set of error microphones. Implementation issues, including loudspeaker placement and error microphone placement, are discussed. Preliminary results from a 9-3/8 inch by 21 inch duct, using 12 loudspeakers and 24 microphones, are presented. These results demonstrate the ability of the control system to generate a user-specified mode while suppressing undesired modes.
Stability analysis of thermocapillary convection in rectangular cavities
Xu, J.; Zebib, A.
1996-12-31
This paper presents stability analysis on thermocapillary convection of acetone (Pr = 4.4) in rectangular cavities using direct numerical simulation. Influence of the Reynolds number (Re) and cavity aspect ratio (Ar) on motion is investigated. Results are exhibited for streamline and isotherm patterns at different values of Re and Ar. Neutral stability curves for transition to time-dependent convection are delineated for this Pr = 4.4 fluid in the Re-Ar plane, and compared with the results for fluids with Pr = 10.0, 6.78 and 1.0. Several interesting features of these diagrams are discussed. One important conclusion the authors have from the comparison is that Ar{sub cr} increases as Pr decreases. Thus, it appears that large values of both Ar and Re are necessary to induce thermocapillary oscillations for small Pr fluids such as liquid metals. On the other hand, energy analysis is performed for the oscillatory flow in the neighborhood of critical points in order to gain insight of mechanisms leading to instability. Results are provided for flows near both critical points with Ar = 3.0.
Visualization of Boiling Phenomena in Inclined Rectangular Gap
J. L. Rempe
2005-05-01
An experimental study was performed to investigate the pool boiling critical heat flux (CHF) in one-dimensional inclined rectangular channels by changing the orientation of a copper test heater assembly. In a pool of saturated water under the atmospheric pressure, the test parameters include the gap sizes of 1, 2, 5, and 10 mm, and the surface orientation angles from the downward-facing position (1800) to the vertical position (90º), respectively. Tests were conducted on the basis of the visualization of boiling phenomena in the narrowly confined channel and open periphery utilizing a high-speed digital camera. To prevent the heat loss from the water pool and copper test heater, a state-of-the-art vacuum pumping technique was introduced. It was observed that the CHF generally decreases as the surface inclination angle increases and as the gap size decreases. In the downward-facing position (180o), however, the vapor movement was enhanced by the gap structure, which produced the opposing result, say, the CHF increases as the gap size decreases. Phenomenological characteristics regarding the interfacial instability of vapor layer were addressed in terms of visualization approaching the CHF. It was found that there exists a transition angle, around which the CHF changes with a rapid slope.
Capillary driven flow of polydimethylsiloxane in open rectangular microchannels.
Sowers, Timothy W; Sarkar, Rohit; Eswarappa Prameela, Suhas; Izadi, Ehsan; Rajagopalan, Jagannathan
2016-06-29
The flow of liquid polydimethylsiloxane (PDMS, Dow Corning Sylgard 184, 10 : 1 base to cross-linker ratio) in open, rectangular silicon microchannels, with and without a coating (100 nm) of poly-tetra-fluoro-ethylene (PTFE), was studied. Photolithographic patterning and etching of silicon wafers was used to create microchannels with a range of widths (∼5-50 μm) and depths (5-20 μm). Experimental PDMS flow rates in both PTFE-coated and uncoated channels were compared to an analytical model based on the work of Lucas and Washburn. The experimental flow rates matched the predicted flow rates reasonably well when the channel aspect ratio (width to depth), p, was less than 2. For channels with p > 2, the observed flow rates progressively lagged model predictions with increasing p. The experimental data, including zero flow rates in certain high aspect ratio PTFE-coated channels, can largely be explained by changes in the front and upper meniscus morphology of the flow as the channel aspect ratio is varied. The results strongly suggest that meniscus morphology needs to be taken into account to accurately model capillary flow in microchannels, especially those with large aspect ratios. PMID:27301750
LEDA 074886: A Remarkable Rectangular-looking Galaxy
NASA Astrophysics Data System (ADS)
Graham, Alister W.; Spitler, Lee R.; Forbes, Duncan A.; Lisker, Thorsten; Moore, Ben; Janz, Joachim
2012-05-01
We report the discovery of an interesting and rare rectangular-shaped galaxy. At a distance of 21 Mpc, the dwarf galaxy LEDA 074886 has an absolute R-band magnitude of -17.3 mag. Adding to this galaxy's intrigue is the presence of an embedded, edge-on stellar disk (of extent 2 R e, disk = 12'' = 1.2 kpc) for which Forbes et al. reported v rot/σ ≈ 1.4. We speculate that this galaxy may be the remnant of two (nearly edge-on) merged disk galaxies in which the initial gas was driven inward and subsequently formed the inner disk, while the stars at larger radii effectively experienced a dissipationless merger event resulting in this "emerald cut galaxy" having very boxy isophotes with a 4/a = -0.05 to -0.08 from 3 to 5 kpc. This galaxy suggests that knowledge from simulations of both "wet" and "dry" galaxy mergers may need to be combined to properly understand the various paths that galaxy evolution can take, with a particular relevance to blue elliptical galaxies.
Single-channel noise reduction using optimal rectangular filtering matrices.
Long, Tao; Chen, Jingdong; Benesty, Jacob; Zhang, Zhenxi
2013-02-01
This paper studies the problem of single-channel noise reduction in the time domain and presents a block-based approach where a vector of the desired speech signal is recovered by filtering a frame of the noisy signal with a rectangular filtering matrix. With this formulation, the noise reduction problem becomes one of estimating an optimal filtering matrix. To achieve such estimation, a method is introduced to decompose a frame of the clean speech signal into two orthogonal components: One correlated and the other uncorrelated with the current desired speech vector to be estimated. Different optimization cost functions are then formulated from which non-causal optimal filtering matrices are derived. The relationships among these optimal filtering matrices are discussed. In comparison with the classical sample-based technique that uses only forward prediction, the block-based method presented in this paper exploits both the forward and backward prediction as well as the temporal interpolation and, therefore, can improve the noise reduction performance by fully taking advantage of the speech property of self correlation. There is also a side advantage of this block-based method as compared to the sample-based technique, i.e., it is computationally more efficient and, as a result, more suitable for practical implementation. PMID:23363124
Strength of Rectangular Flat Plates Under Edge Compression
NASA Technical Reports Server (NTRS)
Schuman, Louis; Back, Goldie
1931-01-01
Flat rectangular plates of duralumin, stainless iron, monel metal, and nickel were tested under loads applied at two opposite edges and acting in the plane of the plate. The edges parallel to the direction of loading were supported in V grooves. The plates were all 24 inches long and varied in width from 4 to 24 inches by steps of 4 inches, and in thickness from 0.015 to 0.095 inch by steps of approximately 0.015 inch. There were also a few 1, 2, 3, and 6 inch wide specimens. The loads were applied in the testing machine at the center of a bar which rested along the top of the plate. Load was applied until the plate failed to take any more load. The tests show that the loads carried by the plates generally reached a maximum for the 8 or 12 inch width and that there was relatively small drop in load for the greater widths. Deflection and set measurement perpendicular to the plane of the plate were taken and the form of the buckle determined. The number of buckles were found to correspond in general to that predicted by the theory of buckling of a plate uniformly loaded at two opposite edges and simply supported at the edges.
Experimental study on mixing efficiency in water supply rectangular tanks
NASA Astrophysics Data System (ADS)
Bateman, A.; Medina, V.; Mujal, A.
2009-04-01
Phenomenon of mixing in drinking water storage tanks and reservoirs has a direct effect on the quality of water. Creation of poor mixing zones and volume stratification can have negative effects in public health. The design of a storage tank must consider the conditions of the inlet and outlets, and also their orientation (vertical or horizontal) to prevent the formation of these zones. Experiments done in a reduced scaled-model with a rectangular base and three different inlets (two waterfalls and a pipe inlet) had the objective to decide which of these inlets achieved the best mixing efficiency. Four situations were considered while three entrances, two unsteady: filling and drawing, and two steady with different outlets. Moreover the effects of columns that support the roof of the tank were studied by running the three entrances with and without columns in the four situations. Neglecting the viscous scale effects, the time taken to mix the volume stored depends on the distance between the inlet and the opposite wall as though as its orientation. Taking into account the whole tank columns have a negative effect on mixing efficiency although they divide the flux and create local zones of turbulence around them, increasing local mixing. Using a digital treating image technique the results are found in a quantitative way.
On the electromagnetic scattering from infinite rectangular conducting grids
NASA Technical Reports Server (NTRS)
Christodoulou, C.
1985-01-01
The study and development of two numerical techniques for the analysis of electromagnetic scattering from a rectangular wire mesh are described. Both techniques follow from one basic formulation and they are both solved in the spectral domain. These techniques were developed as a result of an investigation towards more efficient numerical computation for mesh scattering. These techniques are efficient for the following reasons: (a1) make use of the Fast Fourier Transform; (b2) they avoid any convolution problems by converting integrodifferential equations into algebraic equations; and (c3) they do not require inversions of any matrices. The first method, the SIT or Spectral Iteration Technique, is applied for regions where the spacing between wires is not less than two wavelengths. The second method, the SDCG or Spectral Domain Conjugate Gradient approach, can be used for any spacing between adjacent wires. A study of electromagnetic wave properties, such as reflection coefficient, induced currents and aperture fields, as functions of frequency, angle of incidence, polarization and thickness of wires is presented. Examples and comparisons or results with other methods are also included to support the validity of the new algorithms.
Deformation of rectangular thin glass plate coated with magnetostrictive material
NASA Astrophysics Data System (ADS)
Wang, Xiaoli; Yao, Youwei; Liu, Tianchen; Liu, Chian; Ulmer, M. P.; Cao, Jian
2016-08-01
As magnetic smart materials (MSMs), magnetostrictive materials have great potential to be selected as coating materials for lightweight x-ray telescope mirrors due to their capability to tune the mirror profile to the desired shape under a magnetic field. To realize this potential, it is necessary to study the deformation of the mirror substrate with the MSM coating subjected to a localized magnetic field. In this paper, an analytical model is developed to calculate the deformation of rectangular coated samples locally affected by magnetostrictive strains driven by an external magnetic field. As a specific case to validate the model, a square glass sample coated with MSMs is prepared, and its deformation is measured in a designed experimental setup by applying a magnetic field. The measured deformation of the sample is compared with the results calculated from the analytical model. The comparison results demonstrate that the analytical model is effective in calculating the deformation of a coated sample with the localized mismatch strains between the film and the substrate. In the experiments, different shape patterns of surface profile changes are achieved by varying the direction of the magnetic field. The analytical model and the experimental method proposed in this paper can be utilized to further guide the application of magnetostrictive coating to deformable lightweight x-ray mirrors in the future.
Propagation of spiral waves pinned to circular and rectangular obstacles
NASA Astrophysics Data System (ADS)
Sutthiopad, Malee; Luengviriya, Jiraporn; Porjai, Porramain; Phantu, Metinee; Kanchanawarin, Jarin; Müller, Stefan C.; Luengviriya, Chaiya
2015-05-01
We present an investigation of spiral waves pinned to circular and rectangular obstacles with different circumferences in both thin layers of the Belousov-Zhabotinsky reaction and numerical simulations with the Oregonator model. For circular objects, the area always increases with the circumference. In contrast, we varied the circumference of rectangles with equal areas by adjusting their width w and height h . For both obstacle forms, the propagating parameters (i.e., wavelength, wave period, and velocity of pinned spiral waves) increase with the circumference, regardless of the obstacle area. Despite these common features of the parameters, the forms of pinned spiral waves depend on the obstacle shapes. The structures of spiral waves pinned to circles as well as rectangles with the ratio w /h ˜1 are similar to Archimedean spirals. When w /h increases, deformations of the spiral shapes are observed. For extremely thin rectangles with w /h ≫1 , these shapes can be constructed by employing semicircles with different radii which relate to the obstacle width and the core diameter of free spirals.
On the structure of an underexpanded rectangular jet
NASA Astrophysics Data System (ADS)
Krothapalli, A.; Hsia, Y.; Baganoff, D.; Karamcheti, K.
1982-07-01
An underexpanded jet of air issuing from a converging rectangular nozzle of moderate aspect ratio was investigated. Schileren pictures of the flow field along with hot-wire measurements in the jet were obtained at different pressure ratios. At the pressure ratio corresponding to the maximum screeching sound, Schlieren photographs show a very strong organized cylindrical wave pattern on either side of the jet, with their respective sources being located at the end of the third shock cell. Associated with this wave pattern is a large increase in the angle of spread of the jet. It is shown that the self excitation helps to induce large-scale vortical motions in the jet both in the plane containing the small dimension of the nozzle and in the plane containing the long dimension of the nozzle. However, the locations of these structures are different in the two planes. Nevertheless, the characteristic Strouhal number corresponding to these large-scale structures in both planes is the same and equal to 0.12. The influence of the self excitation on the mean velocities and rms intensities was also investigated. For the full range of pressure ratios studied, similarity was found in the mean velocity and rms intensity profiles in the two central planes beyond 80 widths downstream of the nozzle exit. However, the shapes of the similarity profiles are different in the two planes.
Granular segregation in quasi-2d rectangular bin
NASA Astrophysics Data System (ADS)
Gharat, Sandip H.; Khakhar, D. V.
2013-06-01
Experiments are carried out in quasi two-dimensional rectangular bin (two vertical glass plate separated by a gap of 10 mm) to study the effect of feed composition on segregation of granular mixtures during heap formation by intermittent feeding. The stainless steel (SS 316) balls of different sizes (1 and 2 mm) are used as model granular materials. The heap is formed by repeatedly pouring a fixed mass of the mixture. Each feeding results in the formation of a layer of the mixture on the surface of the heap. Results presented here are for binary mixtures with different size and equal density. Profiles of the number fraction of big particles along the flow direction averaged across the depth of the layer are plotted. In each layer formed by a pouring, segregation results in the small particles being deposited first. Thus, the small particles are concentrated in the upper part of the layer and the large particles in the lower part with a mixed region between the two. The extent of segregation is found to increase with decrease in concentration of big particles in the mixture.
Permuting sparse rectangular matrices into block-diagonal form
Aykanat, Cevdet; Pinar, Ali; Catalyurek, Umit V.
2002-12-09
This work investigates the problem of permuting a sparse rectangular matrix into block diagonal form. Block diagonal form of a matrix grants an inherent parallelism for the solution of the deriving problem, as recently investigated in the context of mathematical programming, LU factorization and QR factorization. We propose graph and hypergraph models to represent the nonzero structure of a matrix, which reduce the permutation problem to those of graph partitioning by vertex separator and hypergraph partitioning, respectively. Besides proposing the models to represent sparse matrices and investigating related combinatorial problems, we provide a detailed survey of relevant literature to bridge the gap between different societies, investigate existing techniques for partitioning and propose new ones, and finally present a thorough empirical study of these techniques. Our experiments on a wide range of matrices, using state-of-the-art graph and hypergraph partitioning tools MeTiS and PaT oH, revealed that the proposed methods yield very effective solutions both in terms of solution quality and run time.
The effect of riblets in rectangular duct flow
NASA Astrophysics Data System (ADS)
Dean, Brian; Bhushan, Bharat
2012-02-01
Much is known about the benefits of surface structures which mimic the riblets found on the skin of fast swimming sharks. Structures have been fabricated for study and application which replicate and improve upon the natural shape of the shark skin riblets, providing a maximum drag reduction of nearly 10% in external turbulent fluid flow. Mechanisms of fluid drag in turbulent flow and riblet-drag reduction theories from experiment and simulation are discussed. A brief review of riblet performance studies is given, and optimal riblet geometries are defined for external flow. A discussion of the structure of internal turbulent fluid flow is provided, and existing data for riblet drag reduction benefit is presented. A flow cell for studying riblet effects in internal rectangular duct flow is discussed, and data collected using several riblet surfaces fabricated for the flow cell is presented and analyzed. A discussion of the effects of the riblets on fluid flow is given, and conclusions are drawn about the possible benefits of riblets in internal fluid flow.
Diversity of acoustic streaming in a rectangular acoustofluidic field.
Tang, Qiang; Hu, Junhui
2015-04-01
Diversity of acoustic streaming field in a 2D rectangular chamber with a traveling wave and using water as the acoustic medium is numerically investigated by the finite element method. It is found that the working frequency, the vibration excitation source length, and the distance and phase difference between two separated symmetric vibration excitation sources can cause the diversity in the acoustic streaming pattern. It is also found that a small object in the acoustic field results in an additional eddy, and affects the eddy size in the acoustic streaming field. In addition, the computation results show that with an increase of the acoustic medium's temperature, the speed of the main acoustic streaming decreases first and then increases, and the angular velocity of the corner eddies increases monotonously, which can be clearly explained by the change of the acoustic dissipation factor and shearing viscosity of the acoustic medium with temperature. Commercialized FEM software COMSOL Multiphysics is used to implement the computation tasks, which makes our method very easy to use. And the computation method is partially verified by an established analytical solution. PMID:25541360
The characteristic impedance of large-scale rectangular strip transmission line facilities used for such purposes as EMI susceptibility testing, biological exposures, etc., is discussed. These lines are characterized by a thin center conductor and an air dielectric. Impedance dat...
Generation of transform-limited rectangular pulses in a spectral compressor
Kalashyan, M A; Palandzhyan, K A; Esayan, G L; Muradyan, L Kh
2010-12-09
The generation of 100-fs transform-limited pulses with a rectangular envelope in a spectral compressor is demonstrated experimentally. The pulses are characterised by spectral interferometry. (control of radiation parameters)
On the existence of guided acoustic waves at rectangular anisotropic edges.
Pupyrev, Pavel D; Lomonosov, Alexey M; Nikodijevic, Aleksandar; Mayer, Andreas P
2016-09-01
The existence of acoustic waves with displacements localized at the tip of an isotropic elastic wedge was rigorously proven by Kamotskii, Zavorokhin and Nazarov. This proof, which is based on a variational approach, is extended to rectangular anisotropic wedges. For two high-symmetry configurations of rectangular edges in elastic media with tetragonal symmetry, a criterion is derived that allows identifying the boundary between the regions of existence for wedge modes of even and odd symmetry in regions of parameter space, where even- and odd-symmetry modes do not exist simultaneously. Furthermore, rectangular edges with non-equivalent surfaces are analyzed, and it is shown that at rectangular edges of cubic elastic media with one (110) surface and one (001) surface, a tip-localized guided wave always exists, apart from special cases that are characterized. PMID:27447889
Hubbell rectangular source integral calculation using a fast Chebyshev wavelets method.
Manai, K; Belkadhi, K
2016-07-01
An integration method based on Chebyshev wavelets is presented and used to calculate the Hubbell rectangular source integral. A study of the convergence and the accuracy of the method was carried out by comparing it to previous studies. PMID:27152913
Vibrational analysis of rectangular sandwich plates resting on some elastic point supports
Ichinomiya, Osamu; Maruyama, Koichi; Sekine, Kouji
1995-11-01
An approximate solution of forced-vibration for rectangular sandwich plate resting on some elastic point supports is presented. The sandwich plate has thin, anisotropic composite laminated faces and a thick orthotropic core. The simplified sandwich plate model is used in the analysis. The governing equation of elastically point supported rectangular sandwich plate is obtained by using the Lagrange equation. The steady state response solution to a sinusoidally varying point force is also derived. The response curves of rectangular sandwich plates having CFRP laminated faces and aluminum honeycomb core is calculated. Application examples illustrate the effects of laminate lay-up of face sheets, core material properties and core thickness ratio on the vibration characteristics of rectangular sandwich plate.
Use of Psi Squared and Flux to Simplify Analysis of Transmission past Rectangular Barriers or Wells.
ERIC Educational Resources Information Center
Draper, James E.
1979-01-01
Analyzes the transmission coefficient for a completely general one-dimensional rectangular potential, or well, simply by concentrating on psi squared rather than psi. Gives graphs of all cases of psi squared. (Author/GA)
A buckling analysis for rectangular orthotropic plates with centrally located cutouts
NASA Technical Reports Server (NTRS)
Nemeth, M. P.
1984-01-01
An analysis to obtain the buckling loads of a rectangular orthotropic plate with a centrally located cutout is described. Cutout shapes can be elliptical, circular, rectangular, or square. The boundary conditions considered in the analysis are simply supported unloaded edges and either clamped or simply supported loaded edges. The plate is loaded in uniaxial compression by either uniform edge displacement or uniform edge stress. A computer program that implements this analysis is described, and the program use is demonstrated by sample problems.
Thermal vibration of a rectangular single-layered graphene sheet with quantum effects
Wang, Lifeng Hu, Haiyan
2014-06-21
The thermal vibration of a rectangular single-layered graphene sheet is investigated by using a rectangular nonlocal elastic plate model with quantum effects taken into account when the law of energy equipartition is unreliable. The relation between the temperature and the Root of Mean Squared (RMS) amplitude of vibration at any point of the rectangular single-layered graphene sheet in simply supported case is derived first from the rectangular nonlocal elastic plate model with the strain gradient of the second order taken into consideration so as to characterize the effect of microstructure of the graphene sheet. Then, the RMS amplitude of thermal vibration of a rectangular single-layered graphene sheet simply supported on an elastic foundation is derived. The study shows that the RMS amplitude of the rectangular single-layered graphene sheet predicted from the quantum theory is lower than that predicted from the law of energy equipartition. The maximal relative difference of RMS amplitude of thermal vibration appears at the sheet corners. The microstructure of the graphene sheet has a little effect on the thermal vibrations of lower modes, but exhibits an obvious effect on the thermal vibrations of higher modes. The quantum effect is more important for the thermal vibration of higher modes in the case of smaller sides and lower temperature. The relative difference of maximal RMS amplitude of thermal vibration of a rectangular single-layered graphene sheet decreases monotonically with an increase of temperature. The absolute difference of maximal RMS amplitude of thermal vibration of a rectangular single-layered graphene sheet increases slowly with the rising of Winkler foundation modulus.
The noise reduction potential of dual-stream coaxial rectangular improperly expanded jet flows
NASA Technical Reports Server (NTRS)
Dosanjh, Darshan; Spina, Eric F.
1995-01-01
The research performed began during Spring 1991 as a project to assess the noise reduction potential of rectangular coaxial nozzle configurations for improperly expanded jets. The research plan consisted of: (1) design of coaxial rectangular nozzle configuration by Syracuse graduate research assistant; (2) construction of nozzles by NASA Langley machinists; and (3) acquisition of preliminary acoustic and optical data for a variety of inner and outer jet pressure ratios.
Multi-walled carbon nanotubes with rectangular or square cross-section
NASA Astrophysics Data System (ADS)
Mizutani, Kanako; Kohno, Hideo
2016-06-01
Multi-walled carbon nanotubes with rectangular or square cross-section are formed. The nanotubes are about 50-200 nm in width, and their walls are around 5-30 nm thick. It is very likely that the rectangular cross-section is shaped simultaneously when nanotubes are formed from catalyst Fe nanoparticles during chemical vapor deposition process, and the shape is stabilized by the bonding between adjoining graphene layers in the multi-walled structure.
Critical Heat Flux in Inclined Rectangular Narrow Gaps
Jeong J. Kim; Yong H. Kim; Seong J. Kim; Sang W. Noh; Kune Y. Suh; Joy L. Rempe; Fan-Bill Cheung; Sang B. Kim
2004-06-01
In light of the TMI-2 accident, in which the reactor vessel lower head survived the attack by molten core material, the in-vessel retention strategy was suggested to benefit from cooling the debris through a gap between the lower head and the core material. The GAMMA 1D (Gap Apparatus Mitigating Melt Attack One Dimensional) tests were conducted to investigate the critical heat flux (CHF) in narrow gaps with varying surface orientations. The CHF in an inclined gap, especially in case of the downward-facing narrow gap, is dictated by bubble behavior because the departing bubbles are squeezed. The orientation angle affects the bubble layer and escape of the bubbles from the narrow gap. The test parameters include gap sizes of 1, 2, 5 and 10 mm and the open periphery, and the orientation angles range from the fully downward-facing (180o) to the vertical (90o) position. The 15 ×35 mm copper test section was electrically heated by the thin film resistor on the back. The heater assembly was installed to the tip of the rotating arm in the heated water pool at the atmospheric pressure. The bubble behavior was photographed utilizing a high-speed camera through the Pyrex glass spacer. It was observed that the CHF decreased as the surface inclination angle increased and as the gap size decreased in most of the cases. However, the opposing results were obtained at certain surface orientations and gap sizes. Transition angles, at which the CHF changed in a rapid slope, were also detected, which is consistent with the existing literature. A semi-empirical CHF correlation was developed for the inclined narrow rectangular channels through dimensional analysis. The correlation provides with best-estimate CHF values for realistically assessing the thermal margin to failure of the lower head during a severe accident involving relocation of the core material.
Rapid State Space Modeling Tool for Rectangular Wing Aeroservoelastic Studies
NASA Technical Reports Server (NTRS)
Suh, Peter M.; Conyers, Howard J.; Mavris, Dimitri N.
2014-01-01
This paper introduces a modeling and simulation tool for aeroservoelastic analysis of rectangular wings with trailing edge control surfaces. The inputs to the code are planform design parameters such as wing span, aspect ratio and number of control surfaces. A doublet lattice approach is taken to compute generalized forces. A rational function approximation is computed. The output, computed in a few seconds, is a state space aeroservoelastic model which can be used for analysis and control design. The tool is fully parameterized with default information so there is little required interaction with the model developer. Although, all parameters can be easily modified if desired.The focus of this paper is on tool presentation, verification and validation. This process is carried out in stages throughout the paper. The rational function approximation is verified against computed generalized forces for a plate model. A model composed of finite element plates is compared to a modal analysis from commercial software and an independently conducted experimental ground vibration test analysis. Aeroservoelastic analysis is the ultimate goal of this tool. Therefore the flutter speed and frequency for a clamped plate are computed using V-g and V-f analysis. The computational results are compared to a previously published computational analysis and wind tunnel results for the same structure. Finally a case study of a generic wing model with a single control surface is presented. Verification of the state space model is presented in comparison to V-g and V-f analysis. This also includes the analysis of the model in response to a 1-cos gust.
Rapid State Space Modeling Tool for Rectangular Wing Aeroservoelastic Studies
NASA Technical Reports Server (NTRS)
Suh, Peter M.; Conyers, Howard J.; Mavris, Dimitri N.
2015-01-01
This paper introduces a modeling and simulation tool for aeroservoelastic analysis of rectangular wings with trailing-edge control surfaces. The inputs to the code are planform design parameters such as wing span, aspect ratio, and number of control surfaces. Using this information, the generalized forces are computed using the doublet-lattice method. Using Roger's approximation, a rational function approximation is computed. The output, computed in a few seconds, is a state space aeroservoelastic model which can be used for analysis and control design. The tool is fully parameterized with default information so there is little required interaction with the model developer. All parameters can be easily modified if desired. The focus of this paper is on tool presentation, verification, and validation. These processes are carried out in stages throughout the paper. The rational function approximation is verified against computed generalized forces for a plate model. A model composed of finite element plates is compared to a modal analysis from commercial software and an independently conducted experimental ground vibration test analysis. Aeroservoelastic analysis is the ultimate goal of this tool, therefore, the flutter speed and frequency for a clamped plate are computed using damping-versus-velocity and frequency-versus-velocity analysis. The computational results are compared to a previously published computational analysis and wind-tunnel results for the same structure. A case study of a generic wing model with a single control surface is presented. Verification of the state space model is presented in comparison to damping-versus-velocity and frequency-versus-velocity analysis, including the analysis of the model in response to a 1-cos gust.
Rapid State Space Modeling Tool for Rectangular Wing Aeroservoelastic Studies
NASA Technical Reports Server (NTRS)
Suh, Peter M.; Conyers, Howard Jason; Mavris, Dimitri N.
2015-01-01
This report introduces a modeling and simulation tool for aeroservoelastic analysis of rectangular wings with trailing-edge control surfaces. The inputs to the code are planform design parameters such as wing span, aspect ratio, and number of control surfaces. Using this information, the generalized forces are computed using the doublet-lattice method. Using Roger's approximation, a rational function approximation is computed. The output, computed in a few seconds, is a state space aeroservoelastic model which can be used for analysis and control design. The tool is fully parameterized with default information so there is little required interaction with the model developer. All parameters can be easily modified if desired. The focus of this report is on tool presentation, verification, and validation. These processes are carried out in stages throughout the report. The rational function approximation is verified against computed generalized forces for a plate model. A model composed of finite element plates is compared to a modal analysis from commercial software and an independently conducted experimental ground vibration test analysis. Aeroservoelastic analysis is the ultimate goal of this tool, therefore, the flutter speed and frequency for a clamped plate are computed using damping-versus-velocity and frequency-versus-velocity analysis. The computational results are compared to a previously published computational analysis and wind-tunnel results for the same structure. A case study of a generic wing model with a single control surface is presented. Verification of the state space model is presented in comparison to damping-versus-velocity and frequency-versus-velocity analysis, including the analysis of the model in response to a 1-cos gust.
Aspect Ratio Effects on Fluid Flow Fluctuations in Rectangular Cavities
NASA Astrophysics Data System (ADS)
Kalter, Rudi; Tummers, Mark J.; Wefers Bettink, Jeroen B.; Righolt, Bernhard W.; Kenjereš, Sasa; Kleijn, Chris R.
2014-12-01
The flow from a submerged bifurcated nozzle into rectangular liquid-filled cavities with width-to-thickness ratios W/ T = 6.5, 11, and 18 has been studied using free surface visualization and particle tracking. When W/ T = 11 and when W/ T = 18, self-sustained oscillations of the submerged jets and the free surface are present. When W/ T = 6.5, the self-sustained oscillations are no longer present, but oscillations with the frequency of gravity waves occur. We propose a critical value of W/ T above which self-sustained jet oscillations occur, based on the spreading angle of turbulent jets. When W/ T is larger than this critical value, the shear layers of the jet reach the front and back wall of the cavity before the jet can impinge the side wall, resulting in semi two-dimensional flow in the plane between the front and the back wall. Two-dimensional recirculation zones form alongside the jet leading to the jet oscillations. When W/ T is smaller than this critical value, the jet can develop like a free turbulent jet up to an impingement point at the narrow side wall. When the jet impinges the side wall, flow in the directions parallel and perpendicular to the front and back walls is possible, resulting in complex three-dimensional flow patterns. The critical value for W/ T, based on the known 12 deg spreading angle of turbulent jets is W/ T = 10, which is in good agreement with the experimental results.
On the structure of an underexpanded rectangular jet
NASA Astrophysics Data System (ADS)
Krothapalli, A.; Hsia, Y.; Baganoff, D.; Karamcheti, K.
1982-07-01
An experimental investigation was carried out on an underexpanded jet of air issuing from a converging rectangular nozzle of moderate aspect ratio. Schlieren pictures of the flow field along with hot-wire measurements in the jet were obtained at different pressure ratios. At the pressure ratio corresponding to the maximum screeching sound, Schlieren photographs show a very strong organized cylindrical wave pattern on either side of the jet, with their respective sources being located at the end of the third shock cell. Associated with this wave pattern is a large increase in the angle of spread of the jet. It is shown that the self excitation helps to induce large-scale vortical motions in the jet both in the plane containing the small dimension of the nozzle and in the plane containing the long dimension of the nozzle. However, the locations of these structures are different in the two planes. Nevertheless, the characteristic Strouhal number corresponding to these large-scale structures in both planes is the same and equal to 0.12. The influence of the self excitation on the mean velocities and rms intensities was investigated. For the full range of pressure ratios studied, similarity was found both in the mean velocity and rms intensity profiles in the two central planes beyond 80 widths downstream of the nozzle exit. However, the shapes of the similarity profiles are different in the two planes. For the downstream distances studied, complete axisymmetry (identical mean velocity profiles in both planes) was not found, which suggests it may persist for a large distance downstream of the nozzle exit.
Cholesteric liquid crystals in rectangular microchannels: skyrmions and stripes.
Guo, Yubing; Afghah, Sajedeh; Xiang, Jie; Lavrentovich, Oleg D; Selinger, Robin L B; Wei, Qi-Huo
2016-07-20
In this paper, we present experimental and numerical studies on the microstructures of a cholesteric liquid crystal (CLC) confined in rectangular micron-channels. By using a sequence of microfabrication techniques we fabricated the micro-sized channels with accurately controlled size, aspect ratio and homeotropic surface anchoring. Through optical microscopic studies we established a phase diagram for the liquid crystal defect textures as a function of the channel depth and width. For the channel width larger than ∼2 times the cholesteric pitch p, the LC molecules are oriented primarily vertical to the channel when the channel depth is below 0.75p, form bubble domain defects when the channel depth is around 0.75p, and form stripe textures when the cell depth is above the cholesteric pitch p. In addition, the bubble domain size and the stripe texture periodicity are found to grow with the increase of the channel width. For the channel width smaller than ∼2p and the channel depth between 0.6p to 1.1p, no textures can be observed in the channels. Numerical simulations based on a director tensor relaxation approach yield detailed molecular director fields, and show that the bubble domain defects are baby-skyrmions and that the stripes are the first type of cholesteric fingerprints. A comparison with previous experiments and numerical simulations indicates that the size of the microchannels also influences what type of soliton-like topological textures form in the CLCs confined in the channels. PMID:27396898
Psyplot: Visualizing rectangular and triangular Climate Model Data with Python
NASA Astrophysics Data System (ADS)
Sommer, Philipp
2016-04-01
The development and use of climate models often requires the visualization of geo-referenced data. Creating visualizations should be fast, attractive, flexible, easily applicable and easily reproducible. There is a wide range of software tools available for visualizing raster data, but they often are inaccessible to many users (e.g. because they are difficult to use in a script or have low flexibility). In order to facilitate easy visualization of geo-referenced data, we developed a new framework called "psyplot," which can aid earth system scientists with their daily work. It is purely written in the programming language Python and primarily built upon the python packages matplotlib, cartopy and xray. The package can visualize data stored on the hard disk (e.g. NetCDF, GeoTIFF, any other file format supported by the xray package), or directly from the memory or Climate Data Operators (CDOs). Furthermore, data can be visualized on a rectangular grid (following or not following the CF Conventions) and on a triangular grid (following the CF or UGRID Conventions). Psyplot visualizes 2D scalar and vector fields, enabling the user to easily manage and format multiple plots at the same time, and to export the plots into all common picture formats and movies covered by the matplotlib package. The package can currently be used in an interactive python session or in python scripts, and will soon be developed for use with a graphical user interface (GUI). Finally, the psyplot framework enables flexible configuration, allows easy integration into other scripts that uses matplotlib, and provides a flexible foundation for further development.
Vibration characteristics of rectangular plate in compressible inviscid fluid
NASA Astrophysics Data System (ADS)
Liao, Chan-Yi; Ma, Chien-Ching
2016-02-01
This paper presents a mathematical derivation of the vibration characteristics of an elastic thin plate placed at the bottom of a three dimensional rectangular container filled with compressible inviscid fluid. A set of beam functions is used as the admissible functions of the plate in a fluid-plate system, and the motion of the fluid induced by the deformation of the plate is obtained from a three-dimensional acoustic equation. Pressure from the fluid over the fluid-plate interface is integrated to form a virtual mass matrix. The frequency equation of the fluid-plate system is derived by combining mass, stiffness, and the virtual mass matrix. Solving the frequency equation makes it possible to obtain the dynamic characteristic of the fluid-plate system, such as resonant frequencies, corresponding mode shapes, and velocity of the fluid. Numerical calculations were performed for plates coupled with fluids with various degrees of compressibility to illustrate the difference between compressible and incompressible fluids in a fluid-plate system. The proposed method could be used to predict resonant frequencies and mode shapes with accuracy compared to that of incompressible fluid theory (IFT). The proposed method can be used to analyze cases involving high value of sound velocity, such as incompressible fluids. When the sound velocity approaches infinity, the results obtained for compressible fluids are similar to those of incompressible fluids. We also examined the influence of fluid compressibility on vibration characteristics in which a decrease in sound velocity was shown to correspond to a decrease in resonant frequency. Additional modes, not observed in incompressible fluids, were obtained in cases of low sound velocity, particularly at higher resonant frequencies. Fluid velocity plots clearly reveal that the additional resonant modes can be attributed to the compressible behavior of the fluid.
Magnetic forces produced by rectangular permanent magnets in static microsystems.
Gassner, Anne-Laure; Abonnenc, Mélanie; Chen, Hong-Xu; Morandini, Jacques; Josserand, Jacques; Rossier, Joel S; Busnel, Jean-Marc; Girault, Hubert H
2009-08-21
Finite element numerical simulations were carried out in 2D geometries to map the magnetic field and force distribution produced by rectangular permanent magnets as a function of their size and position with respect to a microchannel. A single magnet, two magnets placed in attraction and in repulsion have been considered. The goal of this work is to show where magnetic beads are preferentially captured in a microchannel. These simulations were qualitatively corroborated, in one geometrical case, by microscopic visualizations of magnetic bead plug formation in a capillary. The results show that the number of plugs is configuration dependent with: in attraction, one plug in the middle of the magnets; in repulsion, two plugs near the edges of the magnets; and with a single magnet, a plug close to the center of the magnet. The geometry of the magnets (h and l are the height and length of the magnets respectively) and their relative spacing s has a significant impact on the magnetic flux density. Its value inside a magnet increases with the h/l ratio. Consequently, bar magnets produce larger and more uniform values than flat magnets. The l/s ratio also influences the magnetic force value in the microchannel, both increasing concomitantly for all the configurations. In addition, a zero force zone in the middle appears in the attraction configuration as the l/s ratio increases, while with a single magnet, the number of maxima and minima goes from one to two, producing two focusing zones instead of only one. PMID:19636467
Development of young oil palm tree recognition using Haar- based rectangular windows
NASA Astrophysics Data System (ADS)
Daliman, S.; Abu-Bakar, S. A. R.; Nor Azam, S. H. Md
2016-06-01
This paper presents development of Haar-based rectangular windows for recognition of young oil palm tree based on WorldView-2 imagery data. Haar-based rectangular windows or also known as Haar-like rectangular features have been popular in face recognition as used in Viola-Jones object detection framework. Similar to face recognition, the oil palm tree recognition would also need a suitable Haar-based rectangular windows that best suit to the characteristics of oil palm tree. A set of seven Haar-based rectangular windows have been designed to better match specifically the young oil palm tree as the crown size is much smaller compared to the matured ones. Determination of features for oil palm tree is an essential task to ensure a high successful rate of correct oil palm tree detection. Furthermore, features that reflects the identification of oil palm tree indicate distinctiveness between an oil palm tree and other objects in the image such as buildings, roads and drainage. These features will be trained using support vector machine (SVM) to model the oil palm tree for classifying the testing set and subimages of WorldView-2 imagery data. The resulting classification of young oil palm tree with sensitivity of 98.58% and accuracy of 92.73% shows a promising result that it can be used for intention of developing automatic young oil palm tree counting.
A PLANAR, RECTANGULAR WAVEGUIDE LAUNCHER AND EXTRACTOR FOR A DUAL-MODED RF POWER DISTRIBUTION SYSTEM
Nantista, Christopher D.
2000-11-21
The desire to reduce the amount of low-loss, circular-waveguide delay line required in a pulse-compressing power distribution system for the Next Linear Collider has led to the pursuit of multi-moded schemes [1]. In such a system, power is delivered to different destinations through the same waveguide via different propagating modes. Current plans [2] utilize two modes, with manipulations done primarily in overmoded rectangular guide. We describe two key components of the system, a four-input/four-output, dual-mode launcher and an extractor for diverting one mode from the delay line to an accelerator feed while allowing the other to pass on to an upstream feed. These novel passive waveguide devices utilize the rectangular TE10 and TE20 modes. Because they must carry up to 600 MW pulsed rf power, H-planar symmetry is maintained in their designs to allow the use of overheight waveguide, and features that invite breakdown, such as coupling slots, irises, and septa, are avoided. Special rectangular-to-circular tapers [3] will be used to convert between the above modes and the circular TE11{sup o} (TE12{sup o}) and TE01{sup o} delay line modes, respectively. Rectangular waveguide for relative ease of handling. Mode converters, including special cross-section tapers [3] will be used to transform between the above circular waveguide modes and the TE20 and TE10 rectangular waveguide modes, respectively.
A computer program for converting rectangular coordinates to latitude-longitude coordinates
Rutledge, A.T.
1989-01-01
A computer program was developed for converting the coordinates of any rectangular grid on a map to coordinates on a grid that is parallel to lines of equal latitude and longitude. Using this program in conjunction with groundwater flow models, the user can extract data and results from models with varying grid orientations and place these data into grid structure that is oriented parallel to lines of equal latitude and longitude. All cells in the rectangular grid must have equal dimensions, and all cells in the latitude-longitude grid measure one minute by one minute. This program is applicable if the map used shows lines of equal latitude as arcs and lines of equal longitude as straight lines and assumes that the Earth 's surface can be approximated as a sphere. The program user enters the row number , column number, and latitude and longitude of the midpoint of the cell for three test cells on the rectangular grid. The latitude and longitude of boundaries of the rectangular grid also are entered. By solving sets of simultaneous linear equations, the program calculates coefficients that are used for making the conversion. As an option in the program, the user may build a groundwater model file based on a grid that is parallel to lines of equal latitude and longitude. The program reads a data file based on the rectangular coordinates and automatically forms the new data file. (USGS)
A Theoretical Investigation of the Input Characteristics of a Rectangular Cavity-Backed Slot Antenna
NASA Technical Reports Server (NTRS)
Cockrell, C. R.
1975-01-01
Equations which represent the magnetic and electric stored energies are derived for an infinite section of rectangular waveguide and a rectangular cavity. These representations which are referred to as being physically observable are obtained by considering the difference in the volume integrals appearing in the complex Poynting theorem. It is shown that the physically observable stored energies are determined by the field components that vanish in a reference plane outside the aperture. These physically observable representations are used to compute the input admittance of a rectangular cavity-backed slot antenna in which a single propagating wave is assumed to exist in the cavity. The slot is excited by a voltage source connected across its center; a sinusoidal distribution is assumed in the slot. Input-admittance calculations are compared with measured data. In addition, input-admittance curves as a function of electrical slot length are presented for several size cavities. For the rectangular cavity backed slot antenna, the quality factor and relative bandwidth were computed independently by using these energy relationships. It is shown that the asymptotic relationship which is usually assumed to exist between the quality bandwidth and the reciprocal of relative bandwidth is equally valid for the rectangular cavity backed slot antenna.
Reorienting strategies in a rectangular array of landmarks by domestic chicks (Gallus gallus).
Pecchia, Tommaso; Vallortigara, Giorgio
2010-05-01
Spatial reorientation in a rectangular array of four landmarks located in the center of a circular enclosure was investigated in domestic chicks (Gallus gallus). One of the landmark possessed unique visual features, indicating the location of a food reward. After training, chicks were tested (a) with the same array as during the training; (b) with four identical landmarks of the type previously nonrewarded, of the type previously rewarded, or of a new type; (c) after having transformed one of the landmarks located at the geometric incorrect location into the type of landmark previously rewarded; or (d) with a fifth landmark of the rewarded type at a new location. Chicks encoded information provided by local featural cues but not the geometric information provided by the shape of the array. Moreover, when trained in a rectangular array of identical landmarks chicks failed to reorient. In a second series of experiments, the array was located in correspondence to the corners of a rectangular enclosure. This time chicks successfully learned to locate the reward using geometric information. However, when the rectangular array was located in the center of a larger rectangular enclosure, chicks failed to reorient, indicating that the geometric information given by the macroscopic layout of arena surfaces was not used to specify different locations. These results suggest that chicks reorient on the basis of a local representation of single landmarks and that encoding of the global aspects of geometry only occurs with respect to the large, extended surfaces of an enclosure. PMID:20476814
NASA Technical Reports Server (NTRS)
Tischler, Adelbert O.
1948-01-01
The performance of an annular combustion chamber from a 24C turbojet engine was investigated over a range of simulated altitudes from 20,000 to 55,000 feet and corrected engine rotor speeds from 6000 to 13,000 rpm at a simulated ram-pressure ratio of 1.04. The purpose of the investigation was to determine the effects on the altitude operational limits, combustor-outlet gas temperature distribution, combustion efficiencies, and combustor inlet-to-outlet total-pressure drops of two changes in the 24C-4B basket air-passage arrangements that were designed to improve combustor-outlet temperature distribution. These changes were: (a) replacement of the downstream secondary air holes with large rectangular slots further upstream (rectangular-slot basket), and (b) enlargement of anticoking holes in the rectangular-slot basket (modified rectangular-slot basket). The results indicate that improved outlet-gas temperature distribution of each succeeding combustor basket investigated was attained at a sacrifice in the altitude limit of operation. The altitude limits of operation of the combustor with the original basket ranged from 34,000 feet at a corrected engine speed of 6000 rpm to a maximum of 52,000 feet at 12 ' 500 rpm. The altitude limits of the rectangular-slot basket were about 2000 feet lower throughout the engine speed range than those of the original basket. The altitude limits of the combustor with the modified rectangular-slot basket were about equivalent to those of the other baskets in the corrected-engine-speed range from 12,000 to 12,500 rpm but were about 10,000 feet lower than those of the original basket in the corrected-engine-speed range from 6000 to 9000 rpm. For the same inlet-air conditions, the combustion efficiencies were highest for the original basket and progressively lower for each of the other two baskets. The combustor inlet-to-outlet pressure drops of all three combustor baskets at the same operating conditions were within +/- 10 percent of
Analysis of pneumatic hammer in rectangular aerostatic thrust bearing with groove
NASA Astrophysics Data System (ADS)
Ma, Wei; Tan, Jiubin; Cui, Jiwen; Liu, Yongmeng
2015-02-01
The pneumatic hammer in rectangular aerostatic thrust bearings with groove is analyzed using perturbation theory. Routh stability criterion was used to evaluate the critical condition of pneumatic hammer in rectangular aerostatic thrust bearings with groove, and the influence of supply pressure, throttle area, groove area, and thickness of film on aerostatic thrust bearings. It was found through analysis that the change rate of stiffness and the volume ratio of aerostatic bearing could be used to analyze the pneumatic hammer in rectangular aerostatic thrust bearings with groove. At a certain film thickness, the stability of aerostatic bearings could be improved by reducing supply pressure, increasing throttle area and decreasing groove area to facilitate the design of a general aerostatic thrust bearing.
Seo, Hyeon-Seok; Boo, Jin-Hyo; Kim, Youn-Jea
2015-10-01
This study numerically investigated the flow characteristics in a rectangular enclosure filled with oil-based ferrofluid (EFH-1, Ferrotec.) under the influence of external magnetic fields. The rectangular enclosure contained obstacles with different shapes, such as a rectangle and a triangle mounted on the top and bottom wall surfaces. In order to generate external magnetic fields, a permanent magnet was located in the lower part of the rectangular enclosure, and its direction was selected to be either horizontal or vertical. Our results showed that the ferrofluid flow fields were affected by the applied external magnetic field direction and eddy flow phenomena in the working fluid were generated in the vicinity of high magnetic flux density distributions, such as at the edge of the permanent magnet. It was also confirmed that the magnetophoretic force distributions in the analysis model played a significant role in the development of the ferrofluid flow fields. PMID:26726349
NASA Technical Reports Server (NTRS)
Lakin, W. D.
1986-01-01
Integrating and differentiating matrices allow the numerical integration and differential of functions whose values are known at points of a discrete grid. Previous derivations of these matrices were restricted to one dimensional grids or to rectangular grids with uniform spacing in at least one direction. Integrating and differentiating matrices were developed for grids with nonuniform spacing in both directions. The use of these matrices as operators to reformulate boundary value problems on rectangular domains as matrix problems for a finite dimensional solution vector is considered. The method requires nonuniform grids which include near boundary points. An eigenvalue problem for the transverse vibrations of a simply supported rectangular plate is solved to illustrate the method.
Numerical Investigation of Flow Around Rectangular Cylinders with and Without Jets
NASA Technical Reports Server (NTRS)
Tiwari, S. N .; Pidugu, S. B.
1999-01-01
The problem of flow past bluff bodies was studied extensively in the past. The problem of drag reduction is very important in many high speed flow applications. Considerable work has been done in this subject area in case of circular cylinders. The present study attempts to investigate the feasibility of drag reduction on a rectangular cylinder by flow injection by flow injection from the rear stagnation region. The physical problem is modeled as two-dimensional body and numerical analysis is carried out with and without trailing jets. A commercial code is used for this purpose. Unsteady computation is performed in case of rectangular cylinders with no trailing jets where as steady state computation is performed when jet is introduced. It is found that drag can be reduced by introducing jets with small intensity in rear stagnation region of the rectangular cylinders.
Numerical simulation of sloshing in rectangular storage tank using coupled FEM-BEM
NASA Astrophysics Data System (ADS)
Saghi, Hassan; Ketabdari, Mohammad Javad
2012-12-01
Sloshing of liquid can increase the dynamic pressure on the storage sidewalls and bottom in tanker ships and LNG careers. Different geometric shapes were suggested for storage tank to minimize the sloshing pressure on tank perimeter. In this research, a numerical code was developed to model liquid sloshing in a rectangular partially filled tank. Assuming the fluid to be inviscid, Laplace equation and nonlinear free surface boundary conditions are solved using coupled FEM-BEM. The code performance for sloshing modeling is validated against available data. To minimize the sloshing pressure on tank perimeter, rectangular tanks with specific volumes and different aspect ratios were investigated and the best aspect ratios were suggested. The results showed that the rectangular tank with suggested aspect ratios, not only has a maximum surrounded tank volume to the constant available volume, but also reduces the sloshing pressure efficiently.
NASA Astrophysics Data System (ADS)
Yeh, Jia-Yi
2013-03-01
In this study, the vibration analysis of sandwich rectangular plates with magnetorheological (MR) elastomer damping treatment is presented. The rectangular plate is combined with a magnetorheological elastomer core layer and a constraining layer to improve the vibration behaviors of the sandwich system. The MR material shows variations in the rheological properties when subjected to varying magnetic fields. Additionally, the MR material exhibits a rapid time response and is applicable to structures or devices when a tunable system is required. The magnetorheological elastomer is found to have a significant effect on the vibration characteristics of the sandwich rectangular plate. The modal damper and the natural frequencies for the sandwich plate system are calculated for various magnetic fields and some designed parameters by utilizing the finite element method. The damping effects of the sandwich plate system can be controlled and changed when different magnetic field strengths are applied.
Uniform patchy and hollow rectangular platelet micelles from crystallizable polymer blends
NASA Astrophysics Data System (ADS)
Qiu, Huibin; Gao, Yang; Boott, Charlotte E.; Gould, Oliver E. C.; Harniman, Robert L.; Miles, Mervyn J.; Webb, Stephen E. D.; Winnik, Mitchell A.; Manners, Ian
2016-05-01
The preparation of colloidally stable, self-assembled materials with tailorable solid or hollow two-dimensional (2D) structures represents a major challenge. We describe the formation of uniform, monodisperse rectangular platelet micelles of controlled size by means of seeded-growth methods that involve the addition of blends of crystalline-coil block copolymers and the corresponding crystalline homopolymer to cylindrical micelle seeds. Sequential addition of different blends yields solid platelet block comicelles with concentric rectangular patches with distinct coronal chemistries. These complex nano-objects can be subject to spatially selective processing that allows their disassembly to form perforated platelets, such as well-defined hollow rectangular rings. The solid and hollow 2D micelles provide a tunable platform for further functionalization and potential for a variety of applications.
Schnurr, Christoph; Nessler, Jochen; König, Dietmar Pierre
2009-12-01
Femoral malrotation in total knee arthroplasty causes flexion gap instability. Conventional instruments mostly reference the posterior condylar angle (PCA). The aim of this study was to verify whether the computer-navigated flexion gap (GAP) method produces a rectangular flexion gap and if a balanced flexion gap could also be achieved by referencing the PCA. A total of 100 knee prostheses were analysed using the navigated GAP method, and flexion gap symmetry along with femoral rotation were recorded. The GAP technique resulted in a rectangular flexion gap with adequate femoral rotational alignment. If the PCA technique had been used, only 51% of the femoral components would have been implanted in correct femoral rotation; the remaining 49% would have implanted with flexion gap instability. The GAP technique produces a rectangular flexion gap. The referencing of the PCA was shown to be less reliable. Thus, modern knee prosthesis instrumentation should not base femoral rotation solely on the PCA. PMID:18956189
Left-Handed Effect of Composite Rectangular SRRs and Its Application in Patch Antennae
NASA Astrophysics Data System (ADS)
Huang, Ming; Zhou, Yue-Qun; Shen, Ting-Gen
2010-01-01
We concentrate on describing the important influence and physical law of the split resonant ring (SRR) based left-handed materials on patch antennae. The finite-difference time-domain method, together with the finite element method is used to study the characteristics of patch antennae based on composite rectangular SRRs. A novel composite rectangular SRR system is formed by assembling the conventional patch antennae and SRRs, it is found that electromagnetic wave resonance occurs near f = 3.15 GHz, the equivalent permittivity and permeability are both negative, and the electromagnetic wave's tunnel effect and evanescent waves' enhancing effect are formed, which can improve the localization extent of electromagnetic wave's energy apparently. Such effects can improve the antenna's radiation gain and its matching condition. The phenomenon indicates that such composite rectangular patch antennae are promising in wireless communications such as mobile phones, satellite communication and aviation.
Design of Three-Dimensional Hypersonic Inlets with Rectangular to Elliptical Shape Transition
NASA Technical Reports Server (NTRS)
Smart, M. K.
1998-01-01
A methodology has been devised for the design of three-dimensional hypersonic inlets which include a rectangular to elliptical shape transition. This methodology makes extensive use of inviscid streamtracing techniques to generate a smooth shape transition from a rectangular-like capture to an elliptical throat. Highly swept leading edges and a significantly notched cowl enable use of these inlets in fixed geometry configurations. The design procedure includes a three dimensional displacement thickness calculation and uses established correlations to check for boundary layer separation due to shock wave interactions. Complete details of the design procedure are presented and the characteristics of a modular inlet with rectangular to elliptical shape transition and a design point of Mach 7.1 are examined. Comparison with a classical two-dimensional inlet optimized for maximum total pressure recovery indicates that this three-dimensional inlet demonstrates good performance even well below its design point.
Uniform patchy and hollow rectangular platelet micelles from crystallizable polymer blends.
Qiu, Huibin; Gao, Yang; Boott, Charlotte E; Gould, Oliver E C; Harniman, Robert L; Miles, Mervyn J; Webb, Stephen E D; Winnik, Mitchell A; Manners, Ian
2016-05-01
The preparation of colloidally stable, self-assembled materials with tailorable solid or hollow two-dimensional (2D) structures represents a major challenge. We describe the formation of uniform, monodisperse rectangular platelet micelles of controlled size by means of seeded-growth methods that involve the addition of blends of crystalline-coil block copolymers and the corresponding crystalline homopolymer to cylindrical micelle seeds. Sequential addition of different blends yields solid platelet block comicelles with concentric rectangular patches with distinct coronal chemistries. These complex nano-objects can be subject to spatially selective processing that allows their disassembly to form perforated platelets, such as well-defined hollow rectangular rings. The solid and hollow 2D micelles provide a tunable platform for further functionalization and potential for a variety of applications. PMID:27151866
Shear flow control of cold and heated rectangular jets by mechanical tabs. Volume 2: Tabulated data
NASA Technical Reports Server (NTRS)
Brown, W. H.; Ahuja, K. K.
1989-01-01
The effects of mechanical protrusions on the jet mixing characteristics of rectangular nozzles for heated and unheated subsonic and supersonic jet plumes were studied. The characteristics of a rectangular nozzle of aspect ratio 4 without the mechanical protrusions were first investigated. Intrusive probes were used to make the flow measurements. Possible errors introduced by intrusive probes in making shear flow measurements were also examined. Several scaled sizes of mechanical tabs were then tested, configured around the perimeter of the rectangular jet. Both the number and the location of the tabs were varied. From this, the best configuration was selected. This volume contains tabulated data for each of the data runs cited in Volume 1. Baseline characteristics, mixing modifications (subsonic and supersonic, heated and unheated) and miscellaneous charts are included.
NASA Technical Reports Server (NTRS)
1985-01-01
Most microscopic cell electrophoretic work depends on the theortical prediction of stationary positions by Smoluchowski and Komagata. Their theoretical solutions are based on the assumption that the electroosmotic flow in a chamber is symmetric. Because experiences with the rectangular chamber indicate that symmetric flow occurs during less than 8% of the experiments, the existing theory for stationary position determination is expanded to include the more general case of asymmetric flow. Smoluchowski's equation for symmetric electroosmotic flow in a rectangular chamber having a width much smaller than its height or length is examined. Smoluchowski's approach is used to approximate stationary positions in rectangular chambers with height/width ratios greater than 40. Support for the theoretical prediction of stationary positions using is given by three types of experimental evidence.
Mundis, Gregory M.; Moazzaz, Payam; Turner, Alexander W. L.; Cornwall, G. Bryan
2015-01-01
Background Expandable cages are gaining popularity in anterior reconstruction of the thoracolumbar spine following corpectomy as they can provide adjustable distraction and deformity correction. Rectangular, rather than circular, endcaps provide increased resistance to subsidence by spanning the apophyseal ring; however their impact on construct stability is not known. The objective of this study was to investigate the contribution of expandable corpectomy cage endcap shape (round vs. rectangular) and fixation method (anterior plate vs. posterior pedicle screws) to the stability of an L1 sub-total corpectomy construct. Methods Eight fresh-frozen cadaveric specimens (T11-L3) were subjected to multi-directional flexibility testing to 6 N·m with a custom spine simulator. Test conditions were: intact, L1 sub-total corpectomy defect, expandable cage (round endcap) alone, expandable cage (round endcap) with anterior plate, expandable cage (round endcap) with bilateral pedicle screws, expandable cage (rectangular endcap) alone, expandable cage (rectangular endcap) with anterior plate, expandable cage (rectangular endcap) with bilateral pedicle screws. Range-of-motion across T12-L2 was measured with an optoelectronic system. Results The expandable cage alone with either endcap provided significant stability to the corpectomy defect, reducing motion to intact levels in flexion-extension with both endcap types, and in lateral bending with rectangular endcaps. Round endcaps allowed greater motion than intact in lateral bending, and axial rotation ROM was greater than intact for both endcaps. Supplemental fixation provided the most rigid constructs, although there were no significant differences between instrumentation or endcap types. Conclusions These results suggest anterior-only fixation may be adequate when using an expandable cage in a sub-total corpectomy application and choice of endcap type may be driven by other factors such as subsidence resistance. PMID:26609508
NASA Astrophysics Data System (ADS)
Chen, Xudong; Zhao, Daomu
2016-08-01
A model of electromagnetic rectangular multi-Gaussian Schell-model (ERMGSM) beams is introduced. Its analytic expression for the elements of the cross-spectral density matrix of such beams passing through oceanic turbulence is derived. It is shown that the rectangular shape of the ERMGSM beams holds a small distance on propagation in oceanic turbulence. The spectral density, the degree of coherence and the degree of polarization of ERMGSM beams are also studied in detail. The results will be helpful for underwater communication by using ERMGSM beams.
A design method for entrance sections of transonic wind tunnels with rectangular cross sections
NASA Technical Reports Server (NTRS)
Lionel, L.; Mcdevitt, J. B.
1975-01-01
A mathematical technique developed to design entrance sections for transonic or high-speed subsonic wind tunnels with rectangular cross sections is discribed. The transition from a circular cross-section setting chamber to a rectangular test section is accomplished smoothly so as not to introduce secondary flows (vortices or boundary-layer separation) into a uniform test stream. The results of static-pressure measurements in the transition region and of static and total-pressure surveys in the test section of a pilot model for a new facility at the Ames Research Center are presented.
OPF by Newton`s method: A comparison between polar and rectangular formulations
Gutierrez, G.; Guzman, C.R.; Chavez, S.; Madrigal, M.; Tovar, J.H.
1998-12-31
The purpose of an Optimal Power Flow (OPF) is to schedule power system controls which optimizes an objective function while at the same time satisfying a set of nonlinear equality and inequality constraints. This problem has been solved by Newton`s approach using polar coordinates to represent power flow equations. In this paper Newton`s method is used to solve the optimal power flow problem, but using rectangular coordinates. Extensive comparison are made against the polar version. The results show superiority in computing time and robustness of the rectangular coordinates Newton`s OPF.
An Experimental Investigation of Rectangular Exhaust-Gas Ejectors Applicable for Engine Cooling
NASA Technical Reports Server (NTRS)
Manganiello, Eugene J; Bogatsky, Donald
1945-01-01
An experimental investigation of rectangular exhaust-gas ejector pumps was conducted to provide data that would serve as a guide to the design of ejector applications for aircraft engines with marginal cooling. The pumping characteristics of rectangular ejectors actuated by the exhaust of a single-cylinder aircraft engine were determined for a range of ejector mixing-section area from 20 to 50 square inches, over-all length from 12 to 42 inches, aspect ratio from 1 to 5, diffusing exit area from 20 to 81 square inches, and exhaust-nozzle aspect ratio from 1 to 42.
A laser beam shaper for homogeneous rectangular illumination based on freeform micro lens array
NASA Astrophysics Data System (ADS)
Chen, En-guo; Huang, Jia-min; Guo, Tai-liang; Wu, Reng-mao
2016-07-01
An effective design method of freeform micro lens array is presented for shaping varied laser beams into prescribed rectangular illumination. The variable separation mapping is applied to design concave freeform surfaces for constructing a freeform lens array. Several dedicated examples show that the designed freeform optical lens array can achieve a prescribed rectangular illumination pattern, especially without considering the initial states of incident laser beams. Both high collection efficiency and good spatial uniformity can be available simultaneously. Tolerance analysis is also performed to demonstrate that this optical device can well avoid fabricating difficulty in actual applications.
Critical combinations of shear and direct axial stress for curved rectangular panels
NASA Technical Reports Server (NTRS)
Schildcrout, Murry; Stein, Manuel
1949-01-01
A solution is presented for the problem of the buckling of curved rectangular panels subjected to combined shear and direct axial stress. Charts giving theoretical critical combinations of shear and direct axial stress are presented for panels having five different length-width ratios. Because the actual critical compressive stress of rectangular panels having substantial curvature is known to be much lower than the theoretical value, a semiempirical method of analysis of curved panels subjected to combined shear and direct axial stress is presented for use in design. (author
Structures of cholesteric liquid crystals confined in rectangular micro-channels
NASA Astrophysics Data System (ADS)
Wei, Qi-Huo; Guo, Yubing; Xiang, Jie; Lavrentovich, Oleg
When cholesteric liquid crystals are confined in various geometries, the interplays between the boundary conditions, the bulk structures and different length scales (pitch, penetration depth, and confinement size) may cause frustration and formation of intriguing topological defects and disclination lines. This paper presents our recent studies on the structures of cholesteric liquid crystals confined in rectangular microchannels with homeotropic alignments. The rectangular microchannels with various sizes and aspect ratios are made in glass substrates by using modern nanofabrication techniques. Detailed liquid crystal structures and their optical characterizations will be presented as a function of the channel depth and width. Work was supported by ACS PRF 53018-ND7.
NASA Astrophysics Data System (ADS)
Cao, Nan; Cao, Fengmei; Lin, Yabin; Bai, Tingzhu; Song, Shengyu
2015-04-01
For a new kind of retina-like senor camera and a traditional rectangular sensor camera, dual cameras acquisition and display system need to be built. We introduce the principle and the development of retina-like senor. Image coordinates transformation and interpolation based on sub-pixel interpolation need to be realized for our retina-like sensor's special pixels distribution. The hardware platform is composed of retina-like senor camera, rectangular sensor camera, image grabber and PC. Combined the MIL and OpenCV library, the software program is composed in VC++ on VS 2010. Experience results show that the system can realizes two cameras' acquisition and display.
Design and experiment study of compact circular-rectangular waveguide mode converter
NASA Astrophysics Data System (ADS)
Zhao, Xuhao; Yuan, Chengwei; Zhang, Qiang; Zhao, Lishan
2016-07-01
A compact mode converter that transforms TM01 circular waveguide mode to TE10 rectangular waveguide mode is investigated. It consists of a circular waveguide with a short circuit terminal and a rectangular waveguide which is perpendicular to the circular waveguide. Simulation results show that conversion efficiency of the mode converter is about 99.8% at central frequency of 1.75 GHz, and the total return loss is approximately -30 dB. The experimental results are well consistent with the computer simulation, which demonstrates the feasibility and high power handling capacity of the mode converter.
The analysis of Raman scattering in a free-electron laser with a rectangular hybrid wiggler
Kordbacheh, A. Shahsavand, M.
2015-10-15
A one dimensional theory of the stimulated Raman backscattering process in a free electron laser with rectangular hybrid wiggler (RHW) is analyzed. The dispersion relation in the rest frame of the electron beam and also a formula for the lab-frame spatial growth rate are derived. A numerical computation of the growth rate for RHW is conducted and a comparison with that for coaxial hybrid wiggler is made away from the resonance. The growth rate is found larger for the rectangular wiggler than for the coaxial wiggler. A much narrower magnetoresonance associated with the third spatial harmonic is also obtained compared to the first one.
Boundary Heat Fluxes for Spectral Radiation from a Uniform Temperature Rectangular Medium
NASA Technical Reports Server (NTRS)
Siegel, Robert
1992-01-01
The effect of spectral behavior is analytically shown for radiation in a 2D rectangular geometry. The solution provides exact boundary heat flux values that can be used for comparison with values obtained from general computer programs. The spectral solution presented can be easily evaluated by numerical integration for complex variations of the spectral absorption coefficient with wavelength.
Effect of wall roughness on liquid oscillations damping in rectangular tanks
NASA Technical Reports Server (NTRS)
Bugg, F. M.
1970-01-01
Tests were conducted in two rectangular glass tanks using silicon carbide grit bonded to walls to determine effect of wall roughness for damping liquid oscillations. Tests included effects of roughness height, roughness location, roughness at various values, amplitude decay, Reynolds number, and boundary layer thickness.
Regenerative Fourier transformation for dual-quadrature regeneration of multilevel rectangular QAM.
Sorokina, Mariia; Sygletos, Stylianos; Ellis, Andrew; Turitsyn, Sergei
2015-07-01
We propose a new nonlinear optical loop mirror based configuration capable of regenerating regular rectangular quadrature amplitude modulated (QAM) signals. The scheme achieves suppression of noise distortion on both signal quadratures through the realization of two orthogonal regenerative Fourier transformations. Numerical simulations show the performance of the scheme for high constellation complexities (including 256-QAM formats). PMID:26125381
Developing Multiplicative Thinking with Rectangular Array Tasks in a Computer Environment
ERIC Educational Resources Information Center
Huang, Amy I-Yu
2013-01-01
This study reports findings from a teaching experiment in which 4th grade children engaged in solving multiplication tasks with rectangular arrays in a computer environment. The environment provided flexible task-solving through dynamic virtual manipulatives (VMs) so children could use their existing knowledge of multiplication to complete array…
NASA Technical Reports Server (NTRS)
Laub, G. H.; Kodani, H. M.
1972-01-01
Wind tunnel tests were conducted on scale models of three rectangular shaped cargo containers to determine the aerodynamic characteristics of these typical externally-suspended helicopter cargo configurations. Tests were made over a large range of pitch and yaw attitudes at a nominal Reynolds number per unit length of 1.8 x one million. The aerodynamic data obtained from the tests are presented.
NASA Technical Reports Server (NTRS)
Burley, J. R., II; Bangert, L. S.; Carlson, J. R.
1986-01-01
An investigation was conducted in the static-test facility of the Langley 16-Foot Transonic Tunnel to determine the internal performance of a high-aspect-ratio nonaxisymmetric nozzle with five circular-to-rectangular transition ducts of varying design. Nozzle pressure ratio was varied from 1.5 to 5.3, and nozzle performance parameters were recorded.
ERIC Educational Resources Information Center
Niketic, Nemanja; Milanovic, Vitomir; Radovanovic, Jelena
2012-01-01
In this paper we provide a detailed analysis of the energy position and type of transmission maxima in rectangular quantum wells (QWs), taking into consideration the difference of electron effective masses in the barrier and well layers. Particular attention is given to transmission maxima that are less than unity and the implications of effective…
Rise of the main meniscus in rectangular capillaries: Experiments and modeling.
Wu, Pingkeng; Zhang, Hua; Nikolov, Alex; Wasan, Darsh
2016-01-01
The rise of the main meniscus in rectangular capillaries is important in interpreting the phenomenon of fluid flow in porous media. Despite many experimental studies reported in the literature, there is no universal model for the rise of the main meniscus in either rectangular or square capillaries. In this work, we present an extensive experimental study and modeling of the rise of the main meniscus in both square and rectangular capillaries. Experimental work was carried out using three different liquids (water, ethanol, and hexadecane) in borosilicate glass and plastic (polystyrene) capillaries to investigate the effect of the contact angle and capillary size on the equilibrium main meniscus height. A universal model (an extended two-wall model) based on the Laplace equation was developed to predict the equilibrium height of the main meniscus in rectangular capillaries. Results have shown that, in a wide range of capillary sizes and contact angles, the predicted equilibrium heights of the main meniscus are in good agreement with the experimentally measured values. PMID:26402778
Nonlinear Theory of Entrainment in EEG Under Photo-Stimulation by Periodic Rectangular Pulse
NASA Astrophysics Data System (ADS)
Konno, H.; Chatani, H.; Sakata, A.; Tobimatsu, S.
2007-07-01
Nonlinear theory of entrainment is presented based on a generalized Kubo oscillator (GKO) wherein effect of frequency modulation and that of photo-stimulation with periodic rectangular pulse are accounted. It is shown that the GKO model gives qualitative properties of nonlinear responses under the photo-stimulation in human brain.
Technology Transfer Automated Retrieval System (TEKTRAN)
An empirical correlation of volumetric mass transfer coefficient was developed for a pilot scale internal-loop rectangular airlift bioreactor that was designed for biotechnology. The empirical correlation combines classic turbulence theory, Kolmogorov’s isotropic turbulence theory with Higbie’s pen...
Seo, Hyeon-Seok; Boo, Jin-Hyo; Kim, Youn-Jea
2015-11-01
The characteristics of thermomagnetic convective flow in a rectangular enclosure heated from below and filled with oil-based nanofluid (EFH-1, Ferrotec.), so called ferrofluid, were numerically investigated. The enclosure contained obstacles with rectangular or triangular configurations mounted on the top and bottom walls. To generate homogeneous magnetic fields, a permanent magnet with a uniform magnetic field strength of 600 kA/m was located in the lower part of the rectangular enclosure, and specified the horizontal or vertical direction. Coupling calculations between thermal-flow field and magnetic field in the analysis model were performed using the commercial code, COMSOL Multiphysics. Results showed that the ferrofluid flow fields were affected by the applied external magnetic field directions and that the eddy flow phenomena in the rectangular enclosure were generated in the vicinity of the section of high magnetic flux density fields such as the edge of the permanent magnet. The effect of parameters like temperature distributions and local Nusselt number (Nu) profiles on the thermomagnetic convective flow was graphically depicted with various flow conditions. PMID:26726559
Bivariate normal, conditional and rectangular probabilities: A computer program with applications
NASA Technical Reports Server (NTRS)
Swaroop, R.; Brownlow, J. D.; Ashwworth, G. R.; Winter, W. R.
1980-01-01
Some results for the bivariate normal distribution analysis are presented. Computer programs for conditional normal probabilities, marginal probabilities, as well as joint probabilities for rectangular regions are given: routines for computing fractile points and distribution functions are also presented. Some examples from a closed circuit television experiment are included.
The Effects of a Rectangular Rapid-Flashing Beacon on Vehicle Speed
ERIC Educational Resources Information Center
VanWagner, Michelle; Van Houten, Ron; Betts, Brian
2011-01-01
In 2008, nearly 31% of vehicle fatalities were related to failure to adhere to safe vehicle speeds (National Highway Traffic Safety Administration [NHTSA], 2009). The current study evaluated the effect of a rectangular rapid-flashing beacon (RRFB) triggered by excessive speed on vehicle speed using a combined alternating treatments and reversal…
Fast Poisson, Fast Helmholtz and fast linear elastostatic solvers on rectangular parallelepipeds
Wiegmann, A.
1999-06-01
FFT-based fast Poisson and fast Helmholtz solvers on rectangular parallelepipeds for periodic boundary conditions in one-, two and three space dimensions can also be used to solve Dirichlet and Neumann boundary value problems. For non-zero boundary conditions, this is the special, grid-aligned case of jump corrections used in the Explicit Jump Immersed Interface method. Fast elastostatic solvers for periodic boundary conditions in two and three dimensions can also be based on the FFT. From the periodic solvers we derive fast solvers for the new 'normal' boundary conditions and essential boundary conditions on rectangular parallelepipeds. The periodic case allows a simple proof of existence and uniqueness of the solutions to the discretization of normal boundary conditions. Numerical examples demonstrate the efficiency of the fast elastostatic solvers for non-periodic boundary conditions. More importantly, the fast solvers on rectangular parallelepipeds can be used together with the Immersed Interface Method to solve problems on non-rectangular domains with general boundary conditions. Details of this are reported in the preprint The Explicit Jump Immersed Interface Method for 2D Linear Elastostatics by the author.
Evaluation of the Hubbell rectangular source integral using Haar wavelets method
NASA Astrophysics Data System (ADS)
Belkadhi, K.; Manai, K.
2016-05-01
Haar wavelets numerical integration method is exposed and used for evaluating the Hubbell rectangular source integral. The method convergence is studied to get the minimum iteration number for a desired precision. Haar wavelets results are finally compared to those obtained with other integration methods.
NASA Astrophysics Data System (ADS)
Han, Qiang; Du, Xiuli; Zhou, Yihui; Lee, George C.
2013-09-01
To investigate the seismic performance of hollow reinforced concrete (RC) bridge columns of rectangular cross section under constant axial load and cyclically biaxial bending, five specimens were tested. A parametric study is carried out for different axial load ratios, longitudinal reinforcement ratios and lateral reinforcement ratios. The experimental results showed that all tested specimens failed in the flexural failure mode and their ultimate performance was dominated by flexural capacity, which is represented by the rupture/buckling of tensile longitudinal rebars at the bottom of the bridge columns. Biaxial force and displacement hysteresis loops showed significant stiffness and strength degradations, and the pinching effect and coupling interaction effect of both directions severely decrease the structural seismic resistance. However, the measured ductility coefficient varying from 3.5 to 5.7 and the equivalent viscous damping ratio varying from 0.19 and 0.26 can meet the requirements of the seismic design. The hollow RC rectangular bridge columns with configurations of lateral reinforcement in this study have excellent performance under bidirectional earthquake excitations, and may be considered as a substitute for current hollow RC rectangular section configurations described in the Guideline for Seismic Design of Highway Bridges (JTG/T B02-01-2008). The length of the plastic hinge region was found to approach one sixth of the hollow RC rectangular bridge column height for all specimen columns, and it was much less than those specified in the current JTG/T. Thus, the length of the plastic hinge region is more concentrated for RC rectangular hollow bridge columns.
Segmentation of fat in MRI using a preparatory pair of rectangular RF pulses of opposite direction.
Yee, Seonghwan
2016-05-01
A radiofrequency (RF) pulse-based MRI method is introduced as a novel fat (or water) segmentation method that, unlike the mostly used Dixon's method, does not depend on the echo times. A pair of rectangular RF pulses of opposite direction, when the duration of its rectangular pulse and the off-resonance of its carrier frequency are set to specific values, is proposed as a preparatory RF pulse to be used for the quantitative fat segmentation. The optimal duration of its rectangular pulse and its specific off-resonance were first determined theoretically. Then, such pair of rectangular pulses of opposite direction (PROD pulse) was applied in imaging a few phantoms and volunteers. During the imaging experiments, MRI images were dynamically acquired with the PROD pulse while its carrier frequency was varied in a predefined off-resonance range. By analyzing the dynamically acquired signal changes, the theoretical properties of the PROD pulse were confirmed and the utility of the PROD pulse for the fat segmentation was verified. All MRI scans were performed in a clinical 3T system. The PROD pulse, if the duration of each rectangular pulse was set to 1.66ms and its carrier frequency was set to a specific off-resonance (e.g. ±223.5Hz, or -670.5Hz) in 3T, was effective in optimally modulating MRI signals to be used for the fat-water segmentation. Therefore, the PROD pulse can successfully be used as a preparatory RF pulse in MRI to achieve effective fat (or water) segmentation in MRI. PMID:26612077
Tantawi, Sami G.; Dolgashev, Valery A.; Yeremian, Anahid D.
2016-03-15
A high-power microwave RF window is provided that includes a cylindrical waveguide, where the cylindrical waveguide includes a ceramic disk concentrically housed in a central region of the cylindrical waveguide, a first rectangular waveguide, where the first rectangular waveguide is connected by a first elliptical joint to a proximal end of the cylindrical waveguide, and a second rectangular waveguide, where the second rectangular waveguide is connected by a second elliptical joint to a distal end of the cylindrical waveguide.
NASA Astrophysics Data System (ADS)
Holmberg, Andreas; Karlsson, Mikael; Åbom, Mats
2015-03-01
Scattering matrices are determined experimentally and used to study the low-amplitude interaction, between the acoustic and the hydrodynamic fields in a T-junction of rectangular ducts. In particular, combinations of grazing and bias flows are investigated in the study. It is observed that for all flow combinations, waves incident on the junction at the downstream side only are attenuated, while waves incident at the other branches may be amplified or attenuated, depending on the Strouhal number. When bias in-flow is introduced to a grazing flow, there is first an increase and then a decrease in both amplification and attenuation, as the bias in-flow Mach number is increased. Comparing with T-junctions of circular ducts, the interaction is stronger for rectangular duct junctions.
NASA Technical Reports Server (NTRS)
Kouyoumjian, R. G.; Wang, N.
1974-01-01
The geometrical theory of diffraction (GTD) is employed to analyze the radiation from a perfectly-conducting rectangular cylinder illuminated by an array of line sources. The excitation of the cylinder by a single electric or magnetic current line source is considered first, and a solution which includes contributions from the geometrical optics rays and all singly- and doubly-diffracted rays is obtained. A new diffraction coefficient valid in the transition regions of the shadow and reflection boundaries is employed to obtain a continuous total field, except for negligible discontinuities in the doubly-diffracted field at its shadow boundaries. Patterns calculated by the GTD method are found to be in excellent agreement with those calculated from an integral equation formulation. Using superposition the solution for array or aperture excitation of the rectangular cylinder is obtained. A computer program for this solution is included.
A hybrid representation of the Green's function in an overmoded rectangular cavity
NASA Astrophysics Data System (ADS)
Wu, Doris I.; Chang, David C.
1988-09-01
A hybrid ray-mode representation of the Green's function in a rectangular cavity is developed using the finite Poisson summation formula. To obtain a numerically efficient scheme for computing the field generated by a point source in a large rectangular cavity, the conventional modal representation of the Green's function is modified in such a way that all the modes near resonance are retained while the truncated remainder of the mode series is expressed in terms of a weighted contribution of rays. For an electrically large cavity, the contribution of rays from distant images becomes small; therefore, the ray sum can be approximated by one or two dominant terms without a loss of numerical accuracy. To illustrate the accuracy and the computational simplification of this ray-mode representation, numerical examples are included with the conventional mode series (summed at the expense of long computation time) serving as a reference.
Synthesis and Raman spectrum of crystalline indium oxide micro-rods with rectangular cross-section
Yadav, Kavita Mehta, B. R. Singh, J. P.
2014-04-24
Indium oxide (IO) micro-rods with rectangular cross section were synthesized without catalyst in chemical vapor deposition (CVD) system by carbothermal reduction of indium oxide at 900 °C. The rectangular micro-rods (RMRs) were grown on Si substrate in presence of water vapors and Ar atmosphere. Water was used as oxidizing reagent which controls the In/O stoichiometry in RMRs. The IO RMRs have dimensions of about 20 μm in length and about 1 μm width. The growth process involved in formation of RMRs is vapor-solid (VS) mechanism. Raman analysis was performed to obtain the phonon modes of the RMRs and the peaks of Raman spectrum were indexed to the modes being associated with bcc−In{sub 2}O{sub 3}.
High-frequency RCS of open cavities with rectangular and circular cross sections
NASA Technical Reports Server (NTRS)
Ling, Hao; Lee, Shung-Wu; Chou, Ri-Chee
1989-01-01
The radar cross-section (RCS) analysis of open-ended cavities with rectangular and circular cross sections is carried out using the waveguide modal approach and the shooting-and-bouncing ray (SBR) approach. For a cavity opening on the order of ten wavelengths or larger, the comparison between the two approaches is excellent. It is also observed that at lower frequencies the SBR results deviate from the more accurate modal results. On the other hand, the SBR approach allows for greater flexibility in geometrical modeling, and can be applied to problems where waveguide modes cannot be easily found. SBR results for an offset rectangular cavity and a circular cavity with rounded endplate are presented.
NASA Astrophysics Data System (ADS)
Sharma, Aditi; Singh, G.
2009-01-01
In this paper, we have presented the simulation results of a rectangular microstrip patch antenna at terahertz (THz) frequency ranging from 0.7 to 0.85 THz. THz electromagnetic wave can permit more densely packed communication links with increased security of communication transmission. The simulated results such as gain, radiation efficiency and 10 dB impedance bandwidth of rectangular microstrip patch antenna at THz frequencies without shorting post configuration are 3.497 dB, 55.71% and 17.76%, respectively, whereas with shorting post configuration, corresponding parameters are 3.502 dB, 55.88% and 17.27%. The simulation has been performed by using CST Microwave Studio, which is a commercially available electromagnetic simulator based on the method of finite difference time domain technique.
NASA Astrophysics Data System (ADS)
Singh, G.
2010-01-01
The effects of 2-D electromagnetic crystal substrate on the performance of a rectangular microstrip patch antennas at THz frequencies is simulated. Electromagnetic crystal substrate is used to obtain extremely broad-bandwidth with multi-frequency band operation of the proposed microstrip antennas. Multi-frequency band microstrip patch antennas are used in modern communication systems in order to enhance their capacity through frequency reuse. The simulated 10 dB impedance bandwidth of the rectangular patch microstrip antenna is 34.3% at THz frequency (0.6-0.95 THz). The radiation efficiency, gain and directivity of the proposed antenna are presented at different THz frequencies. The simulation has been performed using CST Microwave Studio, which is a commercially available electromagnetic simulator based on finite integral technique.
NASA Astrophysics Data System (ADS)
Young, Frederick J.; Brown, Samuel H.; Sondergaard, Neal A.
1988-05-01
The magnetohydrodynamic equations for temporal transients have been formulated and solved for a liquid metal flowing in a rectangular channel. The rectangular channel was a perfectly conducting moving top wall and a perfectly conducting stationary bottom wall in the presence of an applied external magnetic field aligned perpendicular to the conducting walls. The side walls of the channel are stationary insulators. Calculations show that the temporal transients of the fluid velocity and induced magnetic intensity comprise two exponentially decaying parts. One fast transient is believed to be associated with the propagation of Alven waves and the other a slow transient being the result of viscous and electrical diffusion. Curves of the transients are presented at several stations in the channel.
Stability of Capillary Surfaces in Rectangular Containers: The Right Square Cylinder
NASA Technical Reports Server (NTRS)
Weislogel, M. M.; Hsieh, K. C.
1998-01-01
The linearized governing equations for an ideal fluid are presented for numerical analysis for the stability of free capillary surfaces in rectangular containers against unfavorable disturbances (accelerations,i.e. Rayleigh-Taylor instability). The equations are solved for the case of the right square cylinder. The results are expressed graphically in term of a critical Bond number as a function of system contact angle. A critical wetting phenomena in the corners is shown to significantly alter the region of stability for such containers in contrast to simpler geometries such as the right circular cylinder or the infinite rectangular slot. Such computational results provide additional constraints for the design of fluids systems for space-based applications.
Kim, Ye-Hwan; Jung, Yeon-Gil; Yoon, Gwang Seob; Moon, Jinok; Watanabe, Akira; Naito, Makio; Paik, Ungyu
2012-03-01
Rectangular ceria particles were synthesized using the flash creation method. The influence of the morphology of ceria particles and the surfactant concentration on the removal rate was systematically investigated. These ceria slurries with polymeric surfactant molecules as the passivation agents of Si3N4 film, shows an exceptional non-Prestonian behaviors. The non-Prestonian behavior can be attributed to the increase in the contact area of the ceria particles with the SiO2 film, which is dominated by the morphology of the ceria particles. Force measurements using an atomic force microscope (AFM) at different concentrations of polymeric surfactant molecules was used to identify the interactions between the polymeric molecules and the oxide film and analyze the non-Prestonian behavior of ceria slurry having rectangular abrasives. PMID:22755127
Warm Deep Drawing Of Rectangular Cups With Magnesium Alloy AZ31 Sheets
Ren, L. M.; Palumbo, G.; Tricarico, L.; Zhang, S. H.
2007-05-17
Recently, magnesium alloys have been widely applied in automotive and electronic industries as the lightest weight structural and functional materials. Warm forming of magnesium alloys has attracted much attention due to the very poor formability of Mg alloys at room temperature. The formability of magnesium alloy sheet at elevated temperature is significantly affected by the processing parameters. Among them the forming temperature, the punch speed, the geometrical shape of the blank, the blank holder force and the lubrication are probably the most relevant. In this research, the deep drawing of rectangular cups with AZ31 sheets was conducted at elevated temperatures with different process parameters. The finite element analyses were performed to investigate the effects of the process parameters on the formability of rectangular cup drawing and to predict the process defects during the process. The material yield condition was modeled using the isotropic Von Mises criterion. The flow stress data were obtained from tensile tests.
Flows caused by rise of a rectangular bar partially immersed in shallow water
NASA Astrophysics Data System (ADS)
Kuznetsovaa, V. V.; Ostapenko, V. V.
2016-03-01
The wave flows caused by the vertical rise of a rectangular bar partially immersed in shallow water filling a rectangular prismatic channel with a horizontal bottom are investigated. Such flows are modeled within the framework of the first approximation of the theory of shallow water disregarding the effect of drag, the viscosity of the fluid, and its surface tension. The case is considered when at the second stage of flow at which the edges of the lower surface of the bar start to come out from the water, the pressure in the region of contact of the bar with the fluid is less than atmospheric one. For this case, an explicit formula setting the law of motion of this boundary is obtained.
NASA Astrophysics Data System (ADS)
Tsai, Chia-Nien; Chen, Lien-Wen
2016-07-01
Self-collimation is wave propagation in straight path without diffraction. The performance is evaluated by bandwidth, angular collimating range and straightness of equi-frequency contours. The present study aims to manipulate the self-collimated beam in square-array phononic crystals by means of orientated rectangular inclusions. Finite element simulations are performed to investigate the effects of the aspect ratio and orientation angle of rectangular inclusions on the self-collimated beam. The simulation results show that the proposed design successfully achieves all-angle self-collimation phenomenon. In addition, it also shows that the propagation direction of a self-collimated beam can be effectively manipulated by varying the orientation angle of inclusions. Numerical simulation result of the S-shaped bend demonstrates that acoustic collimated beam can be steered with negligible diffraction. Overall, the proposed design has significant potential for the realization of applications such as collimators, acoustic waveguides and other phononic crystals-based systems.
Attachment-driven morphology evolvement of rectangular ZnO nanowires.
Zhang, Dong-Feng; Sun, Ling-Dong; Yin, Jia-Lu; Yan, Chun-Hua; Wang, Rong-Ming
2005-05-12
The rectangular cross-sectional ZnO nanowires were synthesized in a solution method. An attachment-driven growth mechanism was proposed for the morphology evolvement of ZnO nanocrystals from nanoparticles to nanoplates and eventually to nanowires. Due to the pileup attachment of the nanoplates to recrystallize into nanowires, unique one-dimensional (1D) ZnO nanowires with the rectangular cross section were obtained, which is different from those nanowires in the previous reports. It is the first time the evidence that "oriented attachment" can occur not only for nanoparticles but also for nanoplates was obtained, suggesting that "oriented attachment" is an intrinsic behavior for nanosized materials. According to the growth model proposed based on the direct TEM observations, ZnO nanocrystals can be easily controlled as nanoparticles, nanoplates, or nanowires by tuning the synthetic parameters. PMID:16852043
Aeroelastic Studies of a Rectangular Wing with a Hole: Correlation of Theory and Experiment
NASA Technical Reports Server (NTRS)
Conyers, Howard J.; Dowell, Earl H.; Hall, Kenneth C.
2010-01-01
Two rectangular wing models with a hole have been designed and tested in the Duke University wind tunnel to better understand the effects of damage. A rectangular hole is used to simulate damage. The wing with a hole is modeled structurally as a thin elastic plate using the finite element method. The unsteady aerodynamics of the plate-like wing with a hole is modeled using the doublet lattice method. The aeroelastic equations of motion are derived using Lagrange's equation. The flutter boundary is found using the V-g method. The hole's location effects the wing's mass, stiffness, aerodynamics and therefore the aeroelastic behavior. Linear theoretical models were shown to be capable of predicting the critical flutter velocity and frequency as verified by wind tunnel tests.
Multi-channel quantum dragons from rectangular nanotubes with even-odd structure
NASA Astrophysics Data System (ADS)
Inkoom, Godfred; Novotny, Mark
Recently, a large class of nanostructures called quantum dragons have been discovered theoretically. Quantum dragons are nanostuctures with correlated disorder but have an electron transmission probability (E) =1 for all energies E when connected to idealized leads. Hence for a single channel, the electrical conductance for a two-probe measurement should give the quantum of conductance Go =2e2/h . The time independent Schrödinger equation for the single band tight binding model is solved exactly to obtain (E) . We have generalized the matrix method and the mapping methods of in order to study multi-channel quantum dragons for rectangular nanotubes with even-odd structure. The studies may be relevant for experimental rectangular nanotubes, such as MgO, copper phthalocyanine or some types of graphyne.. Supported in part by NSF Grant DMR-1206233.
Acoustic plane waves incident on an oblique clamped panel in a rectangular duct
NASA Technical Reports Server (NTRS)
Unz, H.; Roskam, J.
1980-01-01
The theory of acoustic plane waves incident on an oblique clamped panel in a rectangular duct was developed from basic theoretical concepts. The coupling theory between the elastic vibrations of the panel (plate) and the oblique incident acoustic plane wave in infinite space was considered in detail, and was used for the oblique clamped panel in the rectangular duct. The partial differential equation which governs the vibrations of the clamped panel (plate) was modified by adding to it stiffness (spring) forces and damping forces. The Transmission Loss coefficient and the Noise Reduction coefficient for oblique incidence were defined and derived in detail. The resonance frequencies excited by the free vibrations of the oblique finite clamped panel (plate) were derived and calculated in detail for the present case.
NASA Technical Reports Server (NTRS)
Jackson, H. W.; Barmatz, M.; Shipley, C.
1988-01-01
The effect of a standing wave field in a rectangular chamber on the shape and location of an acoustically positioned drop or bubble is calculated. The sample deformation and equilibrium position are obtained from an analysis of the spherical harmonic projections of the total surface stress tensor. The method of calculation relies on the assumed condition that the sample is only slightly distorted from a spherical form. The equilibrium location of a levitated drop is combined with a formula introduced by Hasegawa (1979) to calcualte the ka dependence of the radiation force function. The present theory is valid for large as well as small ka values. Calculations in the small ka limit agree with previous theories and experimental results. Examples are presented for nonplane-wave modes as well as plane-wave rectangular modes.
MHD and heat transfer benchmark problems for liquid metal flow in rectangular ducts
Sidorenkov, S.I.; Hua, T.Q.; Araseki, H.
1994-12-31
Liquid metal cooling systems of a self-cooled blanket in a tokamak reactor will likely include channels of rectangular cross section where liquid metal is circulated in the presence of strong magnetic fields. MHD pressure drop, velocity distribution and heat transfer characteristics are important issues in the engineering design considerations. Computer codes for the reliable solution of three-dimensional MHD flow problems are needed for fusion relevant conditions. Argonne National Laboratory and The Efremov Institute have jointly defined several benchmark problems for code validation. The problems, described in this paper, are based on two series of rectangular duct experiments conducted at ANL; one of the series is a joint ANL/Efremov experiment. The geometries consist of variation of aspect ratio and wall thickness (thus wall conductance ratio). The transverse magnetic fields are uniform and nonuniform in the axial direction.
NASA Astrophysics Data System (ADS)
Zhou, Chuanqiang; Gong, Xiangxiang; Qu, Yun; Han, Jie
2016-08-01
A modified interfacial polymerization of aniline is developed to fabricate hydrophobic and adhesive polyaniline (PANI) layer of rectangular microtubes on the glass substrate. The modified method uses pentanol as an organic medium to dissolve aniline monomer, with the water film of oxidant and surfactant on the glass substrate as water phase. The effects of some synthetic parameters (such as monomer concentration, alcohol molecular structure and surfactant type) on the morphology of PANI layer are studied for better understanding the fabrication of PANI nanostructures on the film. The alcohol molecular structure plays key role for the supermolecular assembly of PANI chains into nanostructures, while the surfactant may direct the array and deposition of these nanostructures on the glass substrate. The formation reason of PANI rectangular sub-microtubes is roughly interpreted according to our previous works. Wettability experiment indicates that the as-prepared PANI layer exhibits excellent hydrophobicity and high adhesive properties to water drop.
Implementation of rectangular slit-inserted ultra-wideband tapered slot antenna.
Kim, Sun-Woong; Choi, Dong-You
2016-01-01
In this paper, a tapered slot antenna capable of ultra-wideband communication was designed. In the proposed antenna, rectangular slits were inserted to enhance the bandwidth and reduce the area of the antenna. The rectangular slit-inserted tapered slot antenna operated at a bandwidth of 8.45 GHz, and the bandwidth improved upon the basic tapered slot antenna by 4.72 GHz. The radiation pattern of the antenna was suitable for location recognition in a certain direction owing to an appropriate 3 dB beam width. The antenna gain was analyzed within the proposed bandwidth, and the highest gain characteristic at 7.55 dBi was exhibited at a 5-GHz band. The simulation and measurement results of the proposed tapered slot antenna were similar. PMID:27610306
Scattered acoustic field above a grating of non-parallel rectangular cavities
NASA Astrophysics Data System (ADS)
Khanfir, A.; Faiz, A.; Ducourneau, J.; Chatillon, J.; Lami, S. Skali
2016-01-01
Geometric or acoustical irregularities induces acoustic scattering. In this paper, a generalization of the model proposed by Khanfir et al. [8] (Journal of Sound and Vibration 332 (4) (2013)) to determine the scattered acoustic field above gratings of parallel rectangular cavities is developed, addressing the case of gratings of non-parallel rectangular cavities. The results provided by the model were compared both to numerical results, obtained with the finite element method, and to experimental ones. The observed agreement between the analytical predictions and the numerical and experimental results supports the validity of the proposed model. The coupling between the different cavities was investigated, in order to attain an explanation for its dependence on frequency and on the spacing between cavities.
High-Tc superconducting rectangular microstrip patch covered with a dielectric layer
NASA Astrophysics Data System (ADS)
Bedra, Sami; Fortaki, Tarek
2016-05-01
This paper presents a full-wave method to calculate the resonant characteristics of rectangular microstrip antenna with and without dielectric cover, to explain the difference of performance with temperature between superconducting and normal conducting antenna. Especially the characteristics of high temperature superconducting (HTS) antenna were almost ideal around the critical temperature (Tc). The dyadic Green's functions of the considered structure are efficiently determined in the vector Fourier transform domain. The effect of the superconductivity of the patch is taken into account using the concept of the complex resistive boundary condition. The computed results are found to be in good agreement with results obtained using other methods. Also, the effects of the superstrate on the resonant frequency and bandwidth of rectangular microstrip patch in a substrate-superstrate configuration are investigated. This type of configuration can be used for wider bandwidth by proper selection of superstrate thickness and its dielectric constants.
Natural Frequencies of Rectangular Plate With- and Without-Rotary Inertia
NASA Astrophysics Data System (ADS)
Kalita, Kanak; Haldar, Salil
2016-07-01
A nine-node isoparametric plate element, in conjunction with first-order shear deformation theory, was used for free vibration analysis of rectangular plates. Both thick and thin plate problems were solved for various aspect ratios and boundary conditions. In this work, the primary focus is on the effect of rotary inertia on the natural frequencies of rectangular plates. It is found that rotary inertia significantly affects thick plates, while it can be ignored for thin plates. The numerical convergence is very rapid and based on a comparison with data from the literature; it is proposed that the present formulation can yield highly accurate results. Finally, some numerical solutions are provided here, which may serve as benchmarks for future research on similar problems.
Jalinous, Reza; Lisanby, Sarah H.
2013-01-01
A novel transcranial magnetic stimulation (TMS) device with controllable pulse width (PW) and near rectangular pulse shape (cTMS) is described. The cTMS device uses an insulated gate bipolar transistor (IGBT) with appropriate snubbers to switch coil currents up to 7 kA, enabling PW control from 5 μs to over 100 μs. The near-rectangular induced electric field pulses use 22–34% less energy and generate 67–72% less coil heating compared to matched conventional cosine pulses. CTMS is used to stimulate rhesus monkey motor cortex in vivo with PWs of 20 to 100 μs, demonstrating the expected decrease of threshold pulse amplitude with increasing PW. The technological solutions used in the cTMS prototype can expand functionality, and reduce power consumption and coil heating in TMS, enhancing its research and therapeutic applications. PMID:18232369
Plasmonic band-stop filter with asymmetric rectangular ring for WDM networks
NASA Astrophysics Data System (ADS)
Foroughi Nezhad, Vahid; Abaslou, Siamak; Sadegh Abrishamian, Mohammad
2013-05-01
We proposed a simple asymmetric rectangular band-stop filter based on metal-insulator-metal plasmonic waveguides. It is shown that the performance of the structure as a filter strongly depends on the asymmetry of the rectangular structure. An analytical model based on the analogy between MDM waveguides and the microwave transmission line is used to calculate the resonance wavelengths and explain the behavior of the filter. The bandwidth of spectra can be easily manipulated by adjusting the topological parameters of the filter. It is also demonstrated that by adjusting the bandwidth, the filter can be used for CWDM standard channels. The filter behavior is verified using the numerical finite difference time domain (FDTD) method. The filter is compact and has a footprint of 1 μm × 0.5 μm, which is suitable for integrated optical circuits.
Numerical investigations of turbulent flow past a rectangular cylinder with active flow control
NASA Astrophysics Data System (ADS)
Luong, Sanh B.
The objective of the present research was to investigate the effects of rotating circular cylinders to control high intensity wind load. This research used computational fluid dynamics (CFD) to simulate high Reynolds number gust-like wind load condition for a transient duration of 12 seconds across a three-dimensional rectangular cylinder with dimension of 240x15x7 meters and aspect ratio (Breadth/Height) of 2.3. An array of 20 circular cylinders was positioned along the leading edges of the rectangular bridge cylinder. The research analyzed turbulent flow characteristics across the top and bottom deck surfaces and the development of wake region during two cases: 1) stationary cylinders and 2) rotated cylinders at 400 RPM or velocity ratio of lambda = 1.33. The Strouhal number flow characteristics of 0.08 and 0.17 for aspect ratio of 2 to 3 analyzed in this study were found to be in agreements with published literature.
Competitive growth of In2O3 nanorods with rectangular cross sections
NASA Astrophysics Data System (ADS)
Yan, Youguo; Zhou, Lixia
2008-08-01
In2O3 nanorods with rectangular cross sections have been successfully synthesized using Au as a catalyst through chemical vapor deposition methods. The synthesized nanorods possessed larger size than that of the catalyst particle. The growth process was discussed through detailed theory analysis and experimental validation, and a competitive growth model between axial growth under the vapor liquid solid (VLS) mechanism and lateral growth controlled by the vapor solid (VS) mechanism was proposed to explain the formation of a rectangular cross section and the size change of the nanorods. The research regarding controlled growth under the two mechanisms, viz. VLS and VS, was beneficial for exploration into the controlled growth of complicated functional nanomaterials. Furthermore, the photoluminescence property was also studied.
Peterchev, Angel V; Jalinous, Reza; Lisanby, Sarah H
2008-01-01
A novel transcranial magnetic stimulation (TMS) device with controllable pulse width (PW) and near-rectangular pulse shape (cTMS) is described. The cTMS device uses an insulated gate bipolar transistor (IGBT) with appropriate snubbers to switch coil currents up to 6 kA, enabling PW control from 5 micros to over 100 micros. The near-rectangular induced electric field pulses use 2%-34% less energy and generate 67%-72% less coil heating compared to matched conventional cosine pulses. CTMS is used to stimulate rhesus monkey motor cortex in vivo with PWs of 20 to 100 micros, demonstrating the expected decrease of threshold pulse amplitude with increasing PW. The technological solutions used in the cTMS prototype can expand functionality, and reduce power consumption and coil heating in TMS, enhancing its research and therapeutic applications. PMID:18232369
Qi, Jinyi; Klein, Gregory J.; Huesman, Ronald H.
2000-10-01
A positron emission mammography scanner is under development at our Laboratory. The tomograph has a rectangular geometry consisting of four banks of detector modules. For each detector, the system can measure the depth of interaction information inside the crystal. The rectangular geometry leads to irregular radial and angular sampling and spatially variant sensitivity that are different from conventional PET systems. Therefore, it is of importance to study the image properties of the reconstructions. We adapted the theoretical analysis that we had developed for conventional PET systems to the list mode likelihood reconstruction for this tomograph. The local impulse response and covariance of the reconstruction can be easily computed using FFT. These theoretical results are also used with computer observer models to compute the signal-to-noise ratio for lesion detection. The analysis reveals the spatially variant resolution and noise properties of the list mode likelihood reconstruction. The theoretical predictions are in good agreement with Monte Carlo results.
Inelastic Stability Analysis Of Uniaxially Compressed Flat Rectangular Isotropic CCSS Plate
NASA Astrophysics Data System (ADS)
Ibearugbulem, O. M.; Eziefula, U. G.; Onwuka, D. O.
2015-08-01
This study investigates the inelastic stability of a thin flat rectangular isotropic plate subjected to uniform uniaxial compressive loads using Taylor-Maclaurin series formulated deflection function. The plate has clamped and simply supported edges in both characteristic directions (CCSS boundary conditions). The governing equation is derived using a deformation plasticity theory and a work principle. Values of the plate buckling coefficient are calculated for aspect ratios from 0.1 to 2.0 at intervals of 0.1. The results compared favourably with the elastic stability values and the percentage differences ranged from -0.353% to -7.427%. Therefore, the theoretical approach proposed in this study is recommended for the inelastic stability analysis of thin flat rectangular isotropic plates under uniform in-plane compression.
Modeling of Wave Propagation and Defect Detection in Rectangular Bar Specimens
NASA Astrophysics Data System (ADS)
Guers, Manton J.; Tittmann, Bernhard R.
2010-02-01
In previous papers, a technique utilizing a remote magnetostrictive transducer has been proposed for in-situ measurements of specimens in research reactors. The work presented in this paper examines efforts to model and characterize the technique's ability to detect defects in rectangular bar specimens. A finite element model was used to simulate waveforms recorded in the remote monitoring setup. Since defect detection is of interest, the accuracy of predicted signal amplitudes must be considered and compared to experiments.
Homogenization of rectangular cross-section fibre-reinforced materials: bending-torsion effects
NASA Astrophysics Data System (ADS)
El Jarroudi, Mustapha; Er-Riani, Mustapha
2016-07-01
We study the homogenization of an elastic material in contact with periodic parallel elastic rectangular cross-section fibres of higher rigidity. The interactions between the matrix and the fibres are described by a local adhesion contact law with interfacial adhesive stiffness parameter depending on the period. Assuming that the Lamé constants in the fibres and the stiffness parameter have appropriate orders of magnitude, we derive a class of energy functionals involving extension, flexure and torsion terms.
Boiling Visualization and Critical Heat Flux Phenomena In Narrow Rectangular Gap
J. J. Kim; Y. H. Kim; S. J. Kim; S. W. Noh; K. Y. Suh; J. Rempe; F. B. Cheung; S. B. Kim
2004-12-01
An experimental study was performed to investifate the pool boling critical hear flux (CHF) on one-dimensional inclined rectangular channels with narrow gaps by changing the orientation of a copper test heater assembly. In a pool of saturated water at atmospheric pressure, the test parameters include the gap sizes of 1,2,5, and 10 mm, andthe surface orientation angles from the downward facing position (180 degrees) to the vertical position (90 degress) respectively.
Rectangular-patterned Occipital Alopecia Areata: A Report of Three Cases
Shin, Jaeyong; Jang, Hong Sun; Cho, Sung Bin
2012-01-01
Many reports have described the presence of alopecia areata (AA) associated with other autoimmune diseases, which support the autoimmune nature of AA. Additionally, AA has been reported in association with malignancy as a paraneoplastic symptom. In this report, we describe three patients with diffuse large B-cell lymphoma, alveolar soft part sarcoma, and cavernous sinus arteriovenous fistula with embolization treatment, respectively, who characteristically presented with rectangular-patterned occipital AA. PMID:23180926
NASA Astrophysics Data System (ADS)
McNamara, D. A.; Botha, L.
1989-06-01
The geometric theory of diffraction is used here to examine the effect of finite rectangular groundplane (FGP) size on the sidelobe level (SLL) of a 10-element linear slotted waveguide array. The results provide an idea of the order of magnitude of FGP effects on the near-in SLLs. They provide the designer with an indication of the 'overdesign' required for satisfactory development of an array whose SLL specifications are firm.
Electroporation of subcutaneous mouse tumors by rectangular and trapezium high voltage pulses.
Pliquett, U; Elez, R; Piiper, A; Neumann, E
2004-04-01
The artificial electrotransfer of bioactive agents such as drugs, peptides or therapeutical nucleic acids and oligonucleotides by membrane electroporation (MEP) into single cells and tissue cells requires knowledge of the optimum ranges of the voltage, pulse duration and frequency of the applied pulses. For clinical use, the classical electroporators appear to necessitate some tissue specific presetting of the pulse parameters at the high voltage generator, before the actual therapeutic pulsing is applied. The optimum pulse parameters may be derived from the kinetic normal mode analysis of the current relaxations due to a voltage step (rectangular pulse). Here, the novel method of trapezium test pulses is proposed to rapidly assess the current (I)/voltage (U) characteristics (IUC). The analysis yields practical values for the voltage U(app) between a given electrode distance and pulse duration t(E) of rectangular high voltage (HV) pulses, to be preset for an effective in vivo electroporation of mouse subcutaneous tumors, clamped between two planar plate electrodes of stainless steel. The IUC of the trapezium pulse compares well with the IUC of rectangular pulses of increasing amplitudes. The trapezium pulse phase (s) of constant voltage and 3 ms duration, following the rising ramp phase (r), yields a current relaxation which is similar to the current relaxation during a rectangular pulse of similar duration. The fit of the current relaxation of the trapezium phase (s) to an exponential function and the IUC can be used to estimate the maximum current at a given voltage. The IUC of the falling edge (phase f) of the trapezium pulse serves to estimate the minimum voltage for the exploration of the long-lived electroporation membrane states with consecutive low-voltage (LV) pulses of longer duration, to eventually enhance electrophoretic uptake of ionic substances, initiated by the preceding HV pulses. PMID:14990329
Two Channel Dielectric-Lined Rectangular High Transformer Ratio Accelerator Structure Experiment
Shchelkunov, S. V.; LaPointe, M. A.; Hirshfield, J. L.; Marshall, T. C.; Sotnikov, G.; Gai, Wei; Conde, M.; Power, J.; Mihalcea, D.
2010-11-04
Current status of a two-channel cm-scale rectangular dielectric lined wakefield accelerator structure is described. This structure is installed at the Argonne Wakefield Accelerator facility (AWA), and is presently being evaluated. The device has a transformer ratio of {approx}12.5:1. When driven by a {approx}50 nC single drive bunch it is expected to obtain {approx}6 MV/m acceleration gradient. Related issues are discussed.
NASA Technical Reports Server (NTRS)
Peretti, Linda F.; Dowell, Earl H.
1989-01-01
Asymptotic modal analysis (AMA) is used to study a rectangular cavity with a flexible vibrating portion on one wall and five rigid walls. The agreement between mean square pressure levels of the cavity interior calculated from classical modal analysis and from the AMA method improved as the number of responding modes increased. It is shown that intensification effects were due to both the excitation location and the response location.
NASA Astrophysics Data System (ADS)
Zhurilenko, B. E.
1983-04-01
The spectrum of bulk magnetostatic waves (BMW) and oscillations (BMO) is studied in a rectangular YIG rod during excitation by different antenna systems. Theoretical and experimental results show that, besides the modes whose wave numbers depend on the specimen size, it is possible to excite BMW and BMO modes with various wave field structures. Dependencies and expressions are obtained for these dimensionless modes and oscillations which describe the structure of the wave field both inside and outside the specimen.
Simulation of natural convection in a rectangular loop using finite elements
Pepper, D W; Hamm, L L; Kehoe, A B
1984-01-01
A two-dimensional finite-element analysis of natural convection in a rectangular loop is presented. A psi-omega formulation of the Boussinesque approximation to the Navier-Stokes equation is solved by the false transient technique. Streamlines and isotherms at Ra = 10/sup 4/ are shown for three different modes of heating. The results indicate that corner effects should be considered when modeling flow patterns in thermosyphons.
Interaction of a turbulent-jet noise source with transverse modes in a rectangular duct
NASA Technical Reports Server (NTRS)
Succi, G. P.; Baumeister, K. J.; Ingard, K. U.
1978-01-01
A turbulent jet was used to excite transverse acoustic modes in a rectangular duct. The pressure spectrum showed asymmetric singularities (pressure spikes) at the resonant frequencies of the duct modes. This validates previously published theoretical results. These pressure spikes occurred over a range of jet velocities, orientations, and inlet turbulence levels. At the frequency of the spike, the measured transverse pressure shape matched the resonant mode shape.
Miele, M.; Laymon, D.; Gilkeson, R.; Michelotti, R.
1996-05-01
Rectangular Schlumberger arrays can be used for 2-dimensional lateral profiling of apparent resistivity at a unique current electrode separation, hence single depth of penetration. Numerous apparent resistivity measurements are collected moving the potential electrodes (fixed MN spacing) within a rectangle of defined dimensions. The method provides a fast, cost-effective means for the collection of dense resistivity data to provide high-resolution information on subsurface hydrogeologic conditions. Several rectangular Schlumberger resistivity arrays were employed at Los Alamos National Laboratory (LANL) from 1989 through 1995 in an area adjacent to and downhill from an outfall pipe, septic tank, septic drainfield, and sump. Six rectangular arrays with 2 AB spacings were used to delineate lateral low resistivity anomalies that may be related to fractures that contain clay and/or vadose zone water. Duplicate arrays collected over a three year time period exhibited very good data repeatability. The properties of tritium make it an excellent groundwater tracer. Because tritium was present in discharged water from all of the anthropogenic sources in the vicinity it was used for this purpose. One major low resistivity anomaly correlates with relatively high tritium concentrations in the tuff. This was determined from borehole samples collected within and outside of the anomalous zone. The anomaly is interpreted to be due to fractures that contain clay from the soil profile. The clay was deposited in the fractures by aeolian processes and by surface water infiltration. The fractures likely served as a shallow vadose zone groundwater pathway.
Buckling analysis of moderately thick rectangular plates using coupled displacement field method
NASA Astrophysics Data System (ADS)
Meera Saheb, K.; Aruna, K.
2015-12-01
A simple and efficient coupled displacement field method is developed to study the buckling load parameters of the moderately thick rectangular plates. This method has been successfully applied to study the same for the Timoshenko beams. A single term trigonometric admissible displacement field is assumed for one of the variables, say, the total rotations (in both X, Y directions). Making use of the coupling equations, the spatial variation for the remaining lateral displacement field is derived in terms of the total rotations. The coupled displacement field method makes the energy formulation to contains half the number of unknown independent coefficients, in the case of a rectangular plate, contrary to the conventional Rayleigh-Ritz method. The expressions for the non-dimensional buckling load parameters of the moderately thick rectangular plates with all the edges simply supported are derived. The numerical values of these parameters obtained using the coupled displacement field method match very well with open literature demonstrating the effectiveness of the coupled displacement field method.
Jet Surface Interaction Scrubbing Noise from High Aspect-Ratio Rectangular Jets
NASA Technical Reports Server (NTRS)
Khavaran, Abbas; Bozak, Richard F.
2015-01-01
Concepts envisioned for the future of civil air transport consist of unconventional propulsion systems in the close proximity of the airframe. Distributed propulsion system with exhaust configurations that resemble a high aspect ratio rectangular jet are among geometries of interest. Nearby solid surfaces could provide noise shielding for the purpose of reduced community noise. Interaction of high-speed jet exhaust with structure could also generate new sources of sound as a result of flow scrubbing past the structure, and or scattered noise from sharp edges. The present study provides a theoretical framework to predict the scrubbing noise component from a high aspect ratio rectangular exhaust in proximity of a solid surface. The analysis uses the Greens function (GF) to the variable density Pridmore-Brown equation in a transversely sheared mean flow. Sources of sound are defined as the auto-covariance function of second-rank velocity fluctuations in the jet plume, and are modeled using a RANS-based acoustic analogy approach. Acoustic predictions are presented in an 8:1 aspect ratio rectangular exhaust at three subsonic Mach numbers. The effect of nearby surface on the scrubbing noise component is shown on both reflected and shielded sides of the plate.
NASA Astrophysics Data System (ADS)
Feng, Shuai; Li, Jiewen; Guo, Yuan; Wang, Yiquan
2014-01-01
Multifrequency filtering characteristics of the two-dimensional square-lattice photonic crystal structures with rectangular microcavities are studied. Owing to the different sensitivities of the resonant frequencies to the variation of the rectangle's side length, one resonant frequency can be flexibly adjusted only by changing one of the rectangle's side lengths, while another frequency is immunizing to the variation. So, a two-output-channel frequency filter is designed to allow two frequencies to travel along different channels, and allow the third frequency to travel along both the channels. Based on the low spatial symmetry of rectangular defect, which supports localized modes with different symmetries, together with optimizing the coupling regions between the input waveguide and the rectangular microcavities, the two-output-channel and four-output-channel filters are both achieved, which can select different frequencies to travel along various channels, and share another frequency to travel along every output channel. These kinds of devices have both the abilities of information selecting and sharing carried out by different frequencies, and may have potential applications in the future complex all-optical integrated circuits.
NASA Astrophysics Data System (ADS)
Liu, Y. L.; Zhu, Y. X.; Dong, W. Q.; Yang, H.
2013-01-01
Springback is inevitable for thin-walled rectangular 3A21 tube in rotary-draw bending process, and Young's modulus is a crucial material property parameter affecting springback simulation. Therefore, to improve the springback prediction precision, the variation of Young's modulus with plastic deformation for 3A21 material is studied through a repeated loading-unloading experiment, and a piecewise linear function is given out to describe the relationship between Young's modulus and plastic strain, which is considered into a new material constitutive model combined with the Von-Mises yield function and the Swift isotropic hardening rule. Furthermore, a finite element springback prediction model is established by means of this new constitutive model for rotary-draw bending process of thin-walled rectangular 3A21 tube, and its reliability is validated experimentally. Comparisons between simulation results and experimental data show that, the accuracy of springback prediction can be improved significantly by 18.02% when the variation of Young's modulus is considered. On the basis of the established model, the stress distribution field of thin-walled rectangular 3A21 tube in the whole rotary-draw bending process is obtained and analyzed.
Growth of rectangular hollow tube crystals with rutile-type structure in supercritical fluids
NASA Astrophysics Data System (ADS)
Niwa, K.; Ikegaya, H.; Taguchi, T.; Muto, S.; Tokunaga, T.; Hasegawa, M.
2014-05-01
Super critical fluids are well known as suitable solvents for dissolution and extraction processes, because it exhibits extreme high solubility and reactivity. However further experimental development using supercritical fluid would offer new insight in material science, especially the synthesis and crystal growth of novel materials. We report the successful growth of single crystals with the rutile-type structure (TiO2, Co-doped TiO2, SiO2, GeO2 and SnO2) in supercritical fluids (water or oxygen) using a laser heated diamond-anvil cell up to a pressure of 7 GPa. The resultant product showed the rectangular hollow tube morphology, a several tens of microns in length and a wall thickness of less than 500 nm. TEM analyses demonstrated that this rectangular hollow tube single crystals were surrounded by the {110} faces and grown along the [001] direction. The preferential growth of {110} faces is consistent with the lowest surface energy of {110} faces of the rutile-type structure. In addition, the rapid cooling rate in LHDAC and high solubility of supercritical fluids also play an important role for the formation of the rectangular hollow tube. The details of the synthesis procedure, characterization and growth mechanism are discussed in this paper.
Natural vibration of arbitrary spatially curved rectangular rods with pre-twisted angles
NASA Astrophysics Data System (ADS)
Shih, Y. D.; Chen, J. K.; Chang, Y. C.; Sheng, J. P.
2005-08-01
For the natural vibration of rods of pre-twisted rectangular cross-sections with its centerline spatially curved and twisted arbitrarily, a system of non-dimensional ordinary differential equations is obtained in three translation displacements and three rotational angles of the rod. The eigenvalue problem is solved for the natural frequencies of various pre-twisted angles of the rectangular cross-section area, aspect ratios, slenderness ratio, end conditions and functions of varying cross-section area along the rods by using a numerical method of Runge-Kutta integration. The eigenvalues are determined by the vanishing of a rank-six determinant whose column vectors are obtained at the end of six independent numerical integrations. The differential equations of the adjoint operator system for the eigenvalue problem with its associated boundary conditions are also derived and solved for the eigenvalues to check with that of the vibration system. It is found that the effect of increasing pre-twisted angle of the rod is that the lowest natural frequency of an arbitrary curved rod will asymptotically tend to be a constant, in spite of slenderness ratio, aspect ratio of the rectangular cross-section, E/G ratio, types of end conditions, or the functions of the cross-section area along the rod.
NASA Technical Reports Server (NTRS)
Reichert, B. A.; Hingst, W. R.; Okiishi, T. H.
1991-01-01
Circular-to-rectangular transition ducts are used as exhaust system components of aircraft with rectangular exhaust nozzles. Often, the incoming flow of these transition ducts includes a swirling velocity component remaining from the gas turbine engine. Previous transition duct studies have either not included inlet swirl or when inlet swirl was considered, only overall performance parameters were evaluated. Circular-to-rectangular transition duct flows with and without inlet swirl were explored in order to understand the effect of inlet swirl on the transition duct flow field and to provide detailed duct flow data for comparison with numerical code predictions. A method was devised to create a swirling, solid body rotational flow with minimal associated disturbances. Coefficients based on velocities and total and static pressures measured incross stream planes at four axial locations within the transition duct, along with surface static pressure measurements and surface oil film visualization, are presented for both nonswirling and swirling incoming flow. In both cases the inlet centerline Mach number was 0.35. The Reynolds number based on the inlet centerline velocity and duct inlet diameter was 1,547,000 for nonswirling and 1,366,000 for swirling flow. The maximum swirl angle was 15.6 deg. Two pair of counter-rotating side wall vortices appeared in the duct flow without inlet swirl. These vortices were absent in the swirling incoming flow cases.
From confinement to deconfinement of magnetic monopoles in artificial rectangular spin ices
NASA Astrophysics Data System (ADS)
Nascimento, F. S.; Mól, L. A. S.; Moura-Melo, W. A.; Pereira, A. R.
2012-11-01
We study a frustrated two-dimensional array of dipoles forming an artificial rectangular spin ice with horizontal and vertical lattice parameters given by a and b respectively. We show that the ice regime could be stabilized by appropriate choices for the ratio γ ≡ a/b. Our results show that for \\gamma \\approx \\sqrt {3} , i.e. when the centers of the islands form a triangular lattice, the ground state becomes degenerate. Therefore, while the magnetic charges (monopoles) are excitations connected by an energetic string for general rectangular lattices (including the particular case of a square lattice), they are practically free to move for a special rectangular lattice with \\gamma \\approx \\sqrt {3} . Besides that, our results show that for \\gamma > \\sqrt {3} the system is highly anisotropic in such a way that, even for this range out of the ice regime, the string tension almost vanishes along a particular direction of the array. We also discuss the ground state transition and some thermodynamic properties of the system.
Development of an Empirical Methods for Predicting Jet Mixing Noise of Cold Flow Rectangular Jets
NASA Technical Reports Server (NTRS)
Russell, James W.
1999-01-01
This report presents an empirical method for predicting the jet mixing noise levels of cold flow rectangular jets. The report presents a detailed analysis of the methodology used in development of the prediction method. The empirical correlations used are based on narrow band acoustic data for cold flow rectangular model nozzle tests conducted in the NASA Langley Jet Noise Laboratory. There were 20 separate nozzle test operating conditions. For each operating condition 60 Hz bandwidth microphone measurements were made over a frequency range from 0 to 60,000 Hz. Measurements were performed at 16 polar directivity angles ranging from 45 degrees to 157.5 degrees. At each polar directivity angle, measurements were made at 9 azimuth directivity angles. The report shows the methods employed to remove screech tones and shock noise from the data in order to obtain the jet mixing noise component. The jet mixing noise was defined in terms of one third octave band spectral content, polar and azimuth directivity, and overall power level. Empirical correlations were performed over the range of test conditions to define each of these jet mixing noise parameters as a function of aspect ratio, jet velocity, and polar and azimuth directivity angles. The report presents the method for predicting the overall power level, the average polar directivity, the azimuth directivity and the location and shape of the spectra for jet mixing noise of cold flow rectangular jets.
Approximate natural vibration analysis of rectangular plates with openings using assumed mode method
NASA Astrophysics Data System (ADS)
Cho, Dae Seung; Vladimir, Nikola; Choi, Tae MuK
2013-09-01
Natural vibration analysis of plates with openings of different shape represents an important issue in naval architecture and ocean engineering applications. In this paper, a procedure for vibration analysis of plates with openings and arbitrary edge constraints is presented. It is based on the assumed mode method, where natural frequencies and modes are determined by solving an eigenvalue problem of a multi-degree-of-freedom system matrix equation derived by using Lagrange's equations of motion. The presented solution represents an extension of a procedure for natural vibration analysis of rectangular plates without openings, which has been recently presented in the literature. The effect of an opening is taken into account in an intuitive way, i.e. by subtracting its energy from the total plate energy without opening. Illustrative numerical examples include dynamic analysis of rectangular plates with rectangular, elliptic, circular as well as oval openings with various plate thicknesses and different combinations of boundary conditions. The results are compared with those obtained by the finite element method (FEM) as well as those available in the relevant literature, and very good agreement is achieved.
Rectangular loop-gap resonator with the light access to the sample.
Dutka, Małgorzata; Oleś, Tadeusz; Mossakowski, Marek; Froncisz, Wojciech
2011-05-01
A modified rectangular loop-gap resonator for X-band electron paramagnetic resonance (EPR) studies of aqueous samples, enabling the light access, is described. Changes introduced into rectangular resonator geometry, previously presented in Piasecki et al. (1998) [1], and redesigned coupling structure lead to the better thermal and mechanical stability. The modified structure makes provision for the controlled light access to the sample placed in a flat cell during an EPR experiment. The sensitivity of the resonator for aqueous samples as well as an experimentally tested microwave magnetic field homogeneity are presented. Results of simulations and experimental tests indicate that the presence of light access holes in the resonator's front side does not disturb the uniformity of microwave magnetic field distribution in the nodal plane. The optimal flat cell thickness for unsaturable and saturable aqueous samples has been calculated for this new structure. A modified rectangular geometry of the loop-gap resonator ensures a good performance for aqueous samples allowing its convenient and efficient light illumination during EPR signal recording . PMID:21367631
Spatial DNS of flow transition of a rectangular buoyant reacting free-jet*
NASA Astrophysics Data System (ADS)
Jiang, X.; Luo, K. H.
2001-10-01
This paper describes a spatial direct numerical simulation (DNS) of the flow transition of a buoyant diffusion flame established on a rectangular nozzle with an aspect ratio of 2:1. Combustion is represented by a one-step finite-rate Arrhenius chemistry. Without applying external perturbations, large vortical structures develop naturally in the flow field due to buoyancy effects. The vortex dynamics of the rectangular buoyant reacting jet has been analysed. The interaction between density gradients and gravity initiates the flow vorticity in the cross-streamwise directions. The streamwise vorticity is mainly generated by the vortex stretching. Downstream of the reacting jet, a more disorganized flow regime characterized by small scales has been observed, following the breakdown of the large vortical structures due to three-dimensional vortex interactions. Analysis of the energy spectra shows that the spatially developing reacting jet has a tendency of transition to turbulence under the effects of combustion-induced buoyancy. Buoyancy effects are found to be very important to the formation, development, interaction and breakdown of vortices. In contrast with the relaminarization effects of chemical exothermicity on non-buoyant jet diffusion flames via volumetric expansion and viscous damping, the tendency towards transition to turbulence in buoyant reacting jets is greatly enhanced by the overwhelming buoyancy effects. Calculations of the mean flow property show that the rectangular buoyant reacting jet has a higher entrainment rate than its non-reacting counterpart.
Damage localization in aluminum plate with compact rectangular phased piezoelectric transducer array
NASA Astrophysics Data System (ADS)
Liu, Zenghua; Sun, Kunming; Song, Guorong; He, Cunfu; Wu, Bin
2016-03-01
In this work, a detection method for the damage in plate-like structure with a compact rectangular phased piezoelectric transducer array of 16 piezoelectric elements was presented. This compact array can not only detect and locate a single defect (through hole) in plate, but also identify multi-defects (through holes and surface defect simulated by an iron pillar glued to the plate). The experiments proved that the compact rectangular phased transducer array could detect the full range of plate structures and implement multiple-defect detection simultaneously. The processing algorithm proposed in this paper contains two parts: signal filtering and damage imaging. The former part was used to remove noise from signals. Continuous wavelet transform was applicable to signal filtering. Continuous wavelet transform can provide a plot of wavelet coefficients and the signal with narrow frequency band can be easily extracted from the plot. The latter part of processing algorithm was to implement damage detection and localization. In order to accurately locate defects and improve the imaging quality, two images were obtained from amplitude and phase information. One image was obtained with the Total Focusing Method (TFM) and another phase image was obtained with the Sign Coherence Factor (SCF). Furthermore, an image compounding technique for compact rectangular phased piezoelectric transducer array was proposed in this paper. With the proposed technique, the compounded image can be obtained by combining TFM image with SCF image, thus greatly improving the resolution and contrast of image.
NASA Technical Reports Server (NTRS)
Simons, Rainee N.
2000-01-01
The paper demonstrates suspended rectangular and circular patch antennas with electromagnetically coupled inverted microstrip feed for linear as well as dual linear polarization/frequency applications. The measured results include the return loss and the impedance bandwidth of the antennas.
NASA Technical Reports Server (NTRS)
Brown, W. H.; Ahuja, K. K.
1989-01-01
The effects of mechanical protrusions on the jet mixing characteristics of rectangular nozzles for heated and unheated subsonic and supersonic jet plumes were studied. The characteristics of a rectangular nozzle of aspect ratio 4 without the mechanical protrusions were first investigated. Intrusive probes were used to make the flow measurements. Possible errors introduced by intrusive probes in making shear flow measurements were also examined. Several scaled sizes of mechanical tabs were then tested, configured around the perimeter of the rectangular jet. Both the number and the location of the tabs were varied. From this, the best configuration was selected. The conclusions derived were: (1) intrusive probes can produce significant errors in the measurements of the velocity of jets if they are large in diameter and penetrate beyond the jet center; (2) rectangular jets without tabs, compared to circular jets of the same exit area, provide faster jet mixing; and (3) further mixing enhancement is possible by using mechanical tabs.
Three-dimensional simulation of flows through a rectangular sudden expansion
NASA Astrophysics Data System (ADS)
Sau, Amalendu
1999-10-01
Detailed three-dimensional numerical predictions of the effect of vortex generators on vorticity dynamics and the phenomenon of axis switching are presented for the laminar incompressible flows through a rectangular sudden expansion. As a special case, the axis switching mechanism for flows through a square sudden expansion has also been investigated. The physical domains consist of 2:1 and 1:1 aspect-ratio channels which undergo a sudden expansion such that the backward facing step height is uniform, and equal to 0.75 times the minor width (or width, for the 1:1 aspect-ratio channel) of the inlet channel. The rectangular-shaped protrusions into the flow ("rectangular tabs") are used as vortex generators, placed on the plane of the expansion. Passive forcing was provided by the system geometry and particularly due to the presence of the tabs. Suitable placement of the tabs could either stop or augment the axis switching mechanism. The rectangular vortex rings formed in the shear layer of the expanding jet undergo nonuniform self-induction and a complex three-dimensional deformation of the jet takes place in its downstream location. Such a deformation of the jet leads to the generation of streamwise vortices. Two mechanisms, the ωθ-dynamics, originated from the difference in induced velocities for different segments of a rolled-up azimuthal vortical structure; and the ωz-dynamics, caused due to the induced velocities of streamwise vortex pairs in the flow, co-exist and are identified to be active in flows through a rectangular sudden expansion. The tendency of axis switching initiated by the ωθ-dynamics are either resisted or enhanced by the ωz-dynamics. While ωθ-dynamics is known to be responsible for axis switching in periodically forced asymmetric jets, the ωz-dynamics mostly govern the effect of tabs. The results of the present simulation reveal the flow features closely consistent with the axis switching mechanism suggested by the laboratory flow
NASA Technical Reports Server (NTRS)
Pates, Carl S., III
1991-01-01
A boundary element formulation, along with detailed solution procedure for determining the acoustic field inside a three-dimensional, rectangular duct is presented in this paper. The results of classical and boundary element solutions are compared for a typical rectangular duct by restricting the input frequency in such a way that only plane wave propagation is possible. The effect of changing the type and number of discrete boundary elements on the computed sound pressure levels inside the duct is also presented.
Shirai, Atsushi; Masuda, Sunao
2013-01-01
The authors have previously presented a mathematical model to predict transit time of a neutrophil through an alveolar capillary segment which was modeled as an axisymmetric arc-shaped constriction settled in a cylindrical straight pipe to investigate the influence of entrance curvature of a capillary on passage of the cell. The axially asymmetric cross section of a capillary also influences the transit time because it requires three-dimensional deformation of a cell when it passes through the capillary and could lead to plasma leakage between the cell surface and the capillary wall. In this study, a rectangular channel was introduced, the side walls of which were moderately constricted, as a representative of axially asymmetric capillaries. Dependence of transit time of a neutrophil passing through the constriction on the constriction geometry, i.e., channel height, throat width and curvature radius of the constriction, was numerically investigated, the transit time being compared with that through the axisymmetric model. It was found that the transit time is dominated by the throat hydraulic diameter and curvature radius of the constriction and that the throat aspect ratio little affects the transit time with a certain limitation, indicating that if an appropriate curvature radius is chosen, such a rectangular channel model can be substituted for an axisymmetric capillary model having the same throat hydraulic diameter in terms of the transit time by choosing an appropriate curvature radius. Thus, microchannels fabricated by the photolithography technique, whose cross section is generally rectangular, are expected to be applicable to in vitro model experiments of neutrophil retention and passage in the alveolar capillaries. PMID:23527190
Excitation of a Parallel Plate Waveguide by an Array of Rectangular Waveguides
NASA Technical Reports Server (NTRS)
Rengarajan, Sembiam
2011-01-01
This work addresses the problem of excitation of a parallel plate waveguide by an array of rectangular waveguides that arises in applications such as the continuous transverse stub (CTS) antenna and dual-polarized parabolic cylindrical reflector antennas excited by a scanning line source. In order to design the junction region between the parallel plate waveguide and the linear array of rectangular waveguides, waveguide sizes have to be chosen so that the input match is adequate for the range of scan angles for both polarizations. Electromagnetic wave scattered by the junction of a parallel plate waveguide by an array of rectangular waveguides is analyzed by formulating coupled integral equations for the aperture electric field at the junction. The integral equations are solved by the method of moments. In order to make the computational process efficient and accurate, the method of weighted averaging was used to evaluate rapidly oscillating integrals encountered in the moment matrix. In addition, the real axis spectral integral is evaluated in a deformed contour for speed and accuracy. The MoM results for a large finite array have been validated by comparing its reflection coefficients with corresponding results for an infinite array generated by the commercial finite element code, HFSS. Once the aperture electric field is determined by MoM, the input reflection coefficients at each waveguide port, and coupling for each polarization over the range of useful scan angles, are easily obtained. Results for the input impedance and coupling characteristics for both the vertical and horizontal polarizations are presented over a range of scan angles. It is shown that the scan range is limited to about 35 for both polarizations and therefore the optimum waveguide is a square of size equal to about 0.62 free space wavelength.
A new semi-analytical solution for inertial waves in a rectangular parallelepiped
NASA Astrophysics Data System (ADS)
Nurijanyan, S.; Bokhove, O.; Maas, L. R. M.
2013-12-01
A study of inertial gyroscopic waves in a rotating homogeneous fluid is undertaken both theoretically and numerically. A novel approach is presented to construct a semi-analytical solution of a linear three-dimensional fluid flow in a rotating rectangular parallelepiped bounded by solid walls. The three-dimensional solution is expanded in vertical modes to reduce the dynamics to the horizontal plane. On this horizontal plane, the two dimensional solution is constructed via superposition of "inertial" analogs of surface Poincaré and Kelvin waves reflecting from the walls. The infinite sum of inertial Poincaré waves has to cancel the normal flow of two inertial Kelvin waves near the boundaries. The wave system corresponding to every vertical mode results in an eigenvalue problem. Corresponding computations for rotationally modified surface gravity waves are in agreement with numerical values obtained by Taylor ["Tidal oscillations in gulfs and basins," Proc. London Math. Soc., Ser. 2 XX, 148-181 (1921)], Rao ["Free gravitational oscillations in rotating rectangular basins," J. Fluid Mech. 25, 523-555 (1966)] and also, for inertial waves, by Maas ["On the amphidromic structure of inertial waves in a rectangular parallelepiped," Fluid Dyn. Res. 33, 373-401 (2003)] upon truncation of an infinite matrix. The present approach enhances the currently available, structurally concise modal solution introduced by Maas. In contrast to Maas' approach, our solution does not have any convergence issues in the interior and does not suffer from Gibbs phenomenon at the boundaries. Additionally, an alternative finite element method is used to contrast these two semi-analytical solutions with a purely numerical one. The main differences are discussed for a particular example and one eigenfrequency.
Effects of spoiler surfaces on the aeroelastic behavior of a low-aspect-ratio rectangular wing
NASA Technical Reports Server (NTRS)
Cole, Stanley R.
1990-01-01
An experimental research study to determine the effectiveness of spoiler surfaces in suppressing flutter onset for a low-aspect-ratio, rectangular wing was conducted in the Langley Transonic Dynamics Tunnel (TDT). The wing model used in this flutter test consisted of a rigid wing mounted to the wind-tunnel wall by a flexible, rectangular beam. The flexible beam was connected to the wing root and cantilever mounted to the wind-tunnel wall. The wing had a 1.5 aspect ratio based on wing semispan and a NACA 64A010 airfoil shape. The spoiler surfaces consisted of thin, rectangular aluminum plates that were vertically mounted to the wing surface. The spoiler surface geometry and location on the wing surface were varied to determine the effects of these parameters on the classical flutter of the wing model. Subsonically, the experiment showed that spoiler surfaces increased the flutter dynamic pressure with each successive increase in spoiler height or width. This subsonic increase in flutter dynamic pressure was approximately 15 percent for the maximum height spoiler configuration and for the maximum width spoiler configuration. At transonic Mach numbers, the flutter dynamic pressure conditions were increased even more substantially than at subsonic Mach numbers for some of the smaller spoiler surfaces. But greater than a certain spoiler size (in terms of either height or width) the spoilers forced a torsional instability in the transonic regime that was highly Mach number dependent. This detrimental torsional instability was found at dynamic pressures well below the expected flutter conditions. Variations in the spanwise location of the spoiler surfaces on the wing showed little effect on flutter. Flutter analysis was conducted for the basic configuration (clean wing with all spoiler surface mass properties included). The analysis correlated well with the clean wing experimental flutter results.
Peak axial-velocity decay with multi-element rectangular and triangular nozzles
NASA Technical Reports Server (NTRS)
Groesbeck, D. E.; Vonglahn, U. H.; Huff, R. G.
1972-01-01
The aircraft noise created by the impingement of engine exhaust jet of STOL aircraft with externally blown flaps is discussed. It was determined that the jet-flap interaction noise can be lowered by reducing the impinging velocity of the jet. The reduction must occur at a specific distance from the flap to be effective. The peak axial-velocity decay obtained with rectangular and triangular single element mixer nozzles is presented. Equations are developed for estimating the peak axial velocity decay curves for a wide range of nozzle configurations.
Computation of an Underexpanded 3-D Rectangular Jet by the CE/SE Method
NASA Technical Reports Server (NTRS)
Loh, Ching Y.; Himansu, Ananda; Wang, Xiao Y.; Jorgenson, Philip C. E.
2000-01-01
Recently, an unstructured three-dimensional space-time conservation element and solution element (CE/SE) Euler solver was developed. Now it is also developed for parallel computation using METIS for domain decomposition and MPI (message passing interface). The method is employed here to numerically study the near-field of a typical 3-D rectangular under-expanded jet. For the computed case-a jet with Mach number Mj = 1.6. with a very modest grid of 1.7 million tetrahedrons, the flow features such as the shock-cell structures and the axis switching, are in good qualitative agreement with experimental results.
Chung, Koo-Hyun; Reitsma, Mark G.
2010-02-15
This note outlines a calibration method for atomic force microscope friction measurement that uses the ''pivot'' method of [Bogdanovic et al., Colloids Surf. B 19, 397 (2000)] to generate optical lever sensitivities for known torque applied to rectangular cantilevers. We demonstrate the key calibration parameter to be a linear function of the position at which it is determined along the length of the cantilevers. In this way the optical lever system can be calibrated for cantilever torque by applying loads at locations along the length of a cantilever, away from the integrated tip, so that issues such as tip damage or interference can be avoided.
Computational Test Cases for a Rectangular Supercritical Wing Undergoing Pitching Oscillations
NASA Technical Reports Server (NTRS)
Bennett, Robert M.; Walker, Charlotte E.
1999-01-01
Proposed computational test cases have been selected from the data set for a rectangular wing of panel aspect ratio two with a twelve-percent-thick supercritical airfoil section that was tested in the NASA Langley Transonic Dynamics Tunnel. The test cases include parametric variation of static angle of attack, pitching oscillation frequency, and Mach numbers from subsonic to transonic with strong shocks. Tables and plots of the measured pressures are presented for each case. This report provides an early release of test cases that have been proposed for a document that supplements the cases presented in AGARD Report 702.
Gillman, Eric D.; Amatucci, W. E.
2014-06-15
These experiments utilize a linear hollow cathode to create a dense, rectangular plasma sheet to simulate the plasma layer surrounding vehicles traveling at hypersonic velocities within the Earth's atmosphere. Injection of fine dielectric microparticles significantly reduces the electron density and therefore lowers the electron plasma frequency by binding a significant portion of the bulk free electrons to the relatively massive microparticles. Measurements show that microwave transmission through this previously overly dense, impenetrable plasma layer increases with the injection of alumina microparticles approximately 60 μm in diameter. This method of electron depletion is a potential means of mitigating the radio communications blackout experienced by hypersonic vehicles.
Theory of the special Smith-Purcell radiation from a rectangular grating
Liu, Weihao He, Zhigang Jia, Qika; Li, Weiwei
2015-12-15
The recently uncovered special Smith-Purcell radiation (S-SPR) from the rectangular grating has significantly higher intensity than the ordinary Smith-Purcell radiation (SPR). Its monochromaticity and directivity are also much better. Here we explored the mechanism of the S-SPR by applying the fundamental electromagnetic theory and simulations. We have confirmed that the S-SPR is exactly from the radiating eigen modes of the grating. Its frequency and direction are well correlated with the beam velocity and structure parameters, which indicates its promising applications in tunable wave generation and beam diagnostic.
NASA Astrophysics Data System (ADS)
Sasada, Ichiro
2014-05-01
A method to reduce ac conductive losses in a thin rectangular busbar made of copper is presented. The method is based on a technique, which makes the distribution of the ac current in the cross section of a busbar flatter. Edges of a thin busbar are covered with low permeability magnetic thin layers as caps. The magnetic cap makes the impedance experienced by the current flowing near the edge comparatively larger so that currents cannot get crowded near the edges of a busbar. This method is numerically verified.
Static state estimation of multiterminal DC/AC power system in rectangular co-ordinates
Roy, L.; Sinha, A.K. ); Srivastava, H.N.P. )
1991-01-01
This paper describes a simple, efficient and reliable method for estimating the state of an integrated multiterminal HVDC/AC power system in the rectangular coordinate form. A six variable model is used to represent the converter system. The proposed algorithm performs successfully in obtaining the state of an AC system with a DC link or a multiterminal DC network. It is possible to implement it for an on-line state estimation. Simulation results of a 30-busbar system are presented for illustration.
Sasada, Ichiro
2014-05-07
A method to reduce ac conductive losses in a thin rectangular busbar made of copper is presented. The method is based on a technique, which makes the distribution of the ac current in the cross section of a busbar flatter. Edges of a thin busbar are covered with low permeability magnetic thin layers as caps. The magnetic cap makes the impedance experienced by the current flowing near the edge comparatively larger so that currents cannot get crowded near the edges of a busbar. This method is numerically verified.
Numerical investigation of a space-fractional model of turbulent fluid flow in rectangular ducts
NASA Astrophysics Data System (ADS)
Churbanov, Alexander G.; Vabishchevich, Petr N.
2016-09-01
Models containing fractional derivatives are among the most promising new approaches for description of turbulent flows. In the present work, a steady-state flow in a duct is considered under the condition that the turbulent diffusion is governed by a fractional power of the Laplace operator. To study numerically flows in rectangular channels, finite-difference approximations are employed. The resulting discrete problem is solved by a preconditioned conjugate gradient method. At each iteration, the problem with a fractional power of the grid Laplace operator is solved. Predictions of turbulent flows in ducts at different Reynolds numbers are presented via mean velocity fields.
NASA Technical Reports Server (NTRS)
Park, A.; Dominek, A. K.
1990-01-01
Constitutive parameter extraction from S parameter data using a rectangular waveguide whose cross section is partially filled with a material sample as opposed to being completely filled was examined. One reason for studying a partially filled geometry is to analyze the effect of air gaps between the sample and fixture for the extraction of constitutive parameters. Air gaps can occur in high temperature parameter measurements when the sample was prepared at room temperature. Single port and two port measurement approaches to parameter extraction are also discussed.
Turcksin, B.; Ragusa, J. C.
2013-07-01
A DSA technique to accelerate the iterative convergence of S{sub n} transport solves is derived for bilinear discontinuous (BLD) finite elements on rectangular grids. The diffusion synthetic acceleration equations are discretized using BLD elements by adapting the Modified Interior Penalty technique, introduced in [4] for triangular grids. The MIP-DSA equations are SPD and thus are solved using a preconditioned CG technique. Fourier analyses and implementation of the technique in a BLD S{sub n} transport code show that the technique is stable is effective. (authors)
Polycentric spatial focus of time-reversal electromagnetic field in rectangular conductor cavity.
Chen, Yingming; Wang, Bing-Zhong
2013-11-01
Polycentric focus effect of time-reversal (TR) electromagnetic field is found in a rectangular resonant cavity. Theoretical deduction shows that the effect is due to the mirror symmetry of the cavity and the maximum number of focus points is 27 including 1 main focus point and 26 secondary focus points. A case of 6 focus points is calculated, in which the numerical results are consistent with the theoretical predictions, and particularly the 5 secondary focus points have directly resulted in inaccurate imaging and pulse signal interception. PMID:24216886
NASA Astrophysics Data System (ADS)
Gillman, Eric D.; Amatucci, W. E.
2014-06-01
These experiments utilize a linear hollow cathode to create a dense, rectangular plasma sheet to simulate the plasma layer surrounding vehicles traveling at hypersonic velocities within the Earth's atmosphere. Injection of fine dielectric microparticles significantly reduces the electron density and therefore lowers the electron plasma frequency by binding a significant portion of the bulk free electrons to the relatively massive microparticles. Measurements show that microwave transmission through this previously overly dense, impenetrable plasma layer increases with the injection of alumina microparticles approximately 60 μm in diameter. This method of electron depletion is a potential means of mitigating the radio communications blackout experienced by hypersonic vehicles.
Three dimensional nonlinear analysis of a single-grating rectangular waveguide Cerenkov maser
Xie, Wenqiu; Wang, Zi-Cheng; Luo, Jirun; Zhao, Ding
2015-04-15
A three dimensional (3-D) nonlinear model for illustrating the beam-wave interaction in a single-grating rectangular waveguide sheet-beam Cerenkov maser is presented. The dynamical equations and the equations of motion are solved self-consistently to predict the device performance. Space-charge effects and Ohmic losses are considered in the model. A 1.03 THz backward wave oscillator and a 0.65 THz traveling wave tube are discussed as two illustrative examples.
Adhesion-delamination mechanics of a prestressed rectangular film adhered onto a rigid substrate
NASA Astrophysics Data System (ADS)
Wong, Ming-Fung; Duan, Gang; Wan, Kai-Tak
2007-01-01
A prestressed rectangular film clamped at both ends delaminates from a rigid punch. Based on a thermodynamic energy balance, the delamination mechanics is derived to relate the simultaneous external tensile force applied to the punch, punch displacement, and contact area. Effects of the coupled tensile residual membrane stress and adhesion energy at the punch-film interface are investigated. A "pinch off" (stable shrinking of the contact area to a line) is predicted, contrasting the nonzero "pull-off" radius in a clamped circular film. The model is useful in understanding the behavior of various adhesion-delamination phenomena, especially in one dimensional capacitive microelectromechanical systems radio frequency switches, microstructure network, and nanostructures.
Vector rectangular-shape laser based on reduced graphene oxide interacting with a long fiber taper.
Gao, Lei; Zhu, Tao; Huang, Wei; Zeng, Jing
2014-10-01
A vector dual-wavelength rectangular-shape laser (RSL) based on a long fiber taper deposited with reduced graphene oxide is proposed, where nonlinearity is enhanced due to a large evanescent-field-interacting length and strong field confinement of an 8 mm fiber taper with a waist diameter of 4 μm. Graphene flakes are deposited uniformly on the taper waist with light pressure effect, so this structure guarantees both excellent saturable absorption and high nonlinearity. The RSL with a repetition rate of 7.9 MHz shows fast polarization switching in two orthogonal polarization directions, and temporal and spectral characteristics are investigated. PMID:25322232
Pressure loss through sharp 180 deg turns in smooth rectangular channels
NASA Astrophysics Data System (ADS)
Metzger, D. E.; Plevich, C. W.; Fan, C. S.
1984-07-01
Measured pressure distributions, pressure loss coefficients, and surface streamline visualizations are presented for 180-deg turns in smooth, rectangular cross-section channels. The flow geometry models situations that exist in multipass internal cooling of gas turbine engine airfoils. The turn geometry is characterized by parameters that include the ratio of upstream and downstream channel widths, the nondimensional channel depth, the nondimensional clearance height at the tip of the turn, and the nondimensional corner fillet radius. The present results cover a range of combinations of geometry parameters and Reynolds numbers to aid in prediction of coolant flow rates in present and future cooled airfoil designs.
NASA Technical Reports Server (NTRS)
Zhong, W. F.; Fu, L. S.
1983-01-01
Results are presented for volume integrals associated with the Helmholtz operator, nabla(2) + alpha(2), for the cases of a finite cylindrical region and a region of rectangular parallelepiped. By using appropriate Taylor series expansions and multinomial theorem, these volume integrals are obtained in series form for regions r r' and r 4', where r and r' are distances from the origin to the point of observation and source, respectively. When the wave number approaches zero, the results reduce directly to the potentials of variable densities.
Jet-boundary corrections for reflection-plane models in rectangular wind tunnel
NASA Technical Reports Server (NTRS)
Swanson, Robert S; Toll, Thomas A
1943-01-01
A detailed method for determining the jet-boundary corrections for reflection-plane models in rectangular wind tunnels is presented. The method includes the determination of the tunnel span local distribution and the derivation of equations for the corrections to the angle of attack, the lift and drag coefficients, and the pitching-, rolling-, yawing-, and hinge-moment coefficients. The principle effects of aerodynamic induction and of the boundary-induced curvature of the streamlines have been considered. An example is included to illustrate the method. Numerical values of the more important corrections for reflection-plane models in 7 by 10-foot closed wind tunnels are presented.
Investigations on the amount of downwash behind rectangular and elliptical wings
NASA Technical Reports Server (NTRS)
Muttray, H
1936-01-01
The downwash behind a wing may be computed from the system of vortices created by the wing and which can be substituted for the latter. If the actual rolling-up process of the free vortex sheet is disregarded, the establishment of boundaries for the downwash factors is contingent upon the premise that no rolling up takes place or else that the developed tip vortices start direct on the effective line. The actual downwash factors for the rectangular wing are rather of the approximate magnitude of the values computable with the developed tip vortices starting direct on the wing.
Cooling and Freezing Behaviors of Aqueous Sodium Chloride Solution in a Closed Rectangular Container
NASA Astrophysics Data System (ADS)
Narumi, Akira; Kashiwagi, Takao; Nakane, Ichirou
This paper investigates cooling and freezing behaviors of NaCl aqueous solution in a rectangular container equipped with horizontal partitions of micro porous film in order to determine the mechanisms of heat and mass transfer through cell wall for the purpose of freezing food. For comparison, experiments were performed using partitions of copper plate, no partition, and water. These processes were visualized and measured using real-time laser holographic interferometry. It was found that there was very little difference in the cooling process due to partitions, but that there were significant differences in freezing process when NaCl aqueous solution is used.
Confinement of water droplets on rectangular micro/nano-arrayed surfaces.
Kašpar, Ondřej; Zhang, Hailong; Tokárová, Viola; Boysen, Reinhard I; Suñé, Gemma Rius; Borrise, Xavier; Perez-Murano, Francesco; Hearn, Milton T W; Nicolau, Dan V
2016-07-01
Micro-patterned surfaces with alternate hydrophilic and hydrophobic rectangular areas effectively confine water droplets down to attolitre volumes. The contact angle, volume, and geometry of the confined droplets as a function of the geometry and physico-chemical properties of the confining surfaces have been determined by phenomenological simulations, validated by atomic force microscopy measurements. The combination between experiments and simulations can be used for the purposeful design of arrays with surface-addressable hydrophobicity employed in digital microfluidics and high-throughput screening nanoarrays. PMID:27270705
Anisotropic spin interference in InGaAs/InAlAs rectangular loop arrays
NASA Astrophysics Data System (ADS)
Faniel, S.; Matsuura, T.; Mineshige, S.; Sekine, Y.; Koga, Takaaki
2010-02-01
We report the experimental detection of the anisotropic spin-orbit interaction (SOI) in InGaAs/InAlAs quantum wells, using spin interference experiments in arrays of rectangular loops with their sides aligned to the [1 1 0] and [ 1 1bar 0] crystallographic directions. While the gate voltage is tuned, the time reversal Aharonov-Casher (TRAC) oscillations exhibit higher frequencies when the loops have their longer side along the [1 1 0] direction, clearly highlighting the anisotropy of the SOI. We find that a simple spin interferometer model, including both the Rashba and the Dresselhaus SOIs, reproduces qualitatively the TRAC oscillations.
A Method for Calculation of Hydrodynamic Lift for Submerged and Planing Rectangular Lifting Surfaces
NASA Technical Reports Server (NTRS)
Wadlin, Kenneth L; Christopher, Kenneth W
1958-01-01
A method is presented for the calculation of lift coefficients for rectangular lifting surfaces of aspect ratios from 0.125 to 10 operating at finite depths beneath the water surface, including the zero depth or planing condition. Theoretical values are compared with experimental values obtained at various depths of submergence with lifting surfaces of aspect ratios from 0.125 to 10. The method can also be applied to hydrofoils with dihedral. Lift coefficients computed by this method are in good agreement with existing experimental data for aspect ratios from 0.125 to 10 and dihedral angles up to 10 degrees.
Oscillating-flow loss test results in rectangular heat exchanger passages
NASA Technical Reports Server (NTRS)
Wood, J. Gary
1991-01-01
Test results of oscillating flow losses in rectangular heat exchanger passages of various aspect ratios are given. This work was performed in support of the design of a free-piston Stirling engine (FPSE) for a dynamic space power conversion system. Oscillating flow loss testing was performed using an oscillating flow rig, which was based on a variable stroke and variable frequency linear drive motor. Tests were run over a range of oscillating flow parameters encompassing the flow regimes of the proposed engine design. Test results are presented in both tabular and graphical form and are compared against analytical predictions.
Optimization of two tailored rectangular femtosecond laser pulses in methane dissociation
NASA Astrophysics Data System (ADS)
Sadighi-Bonabi, R.; Dehghani, Z.; Irani, E.
2010-05-01
Based on the quantum mechanics principles and classically calculated dressed potential surfaces by using field assisted dissociation model the dissociation probability for CH4+ molecule exposed with a 100 femtosecond 8 Jcm-2 Ti:sapphire laser pulses is calculated. Using the gradient optimization method two tailored rectangular laser pulses for controlling the dissociation of C-H bond of CH4+ molecule along laser pulse direction is found. In the proposed optimization method, the complicacy of solving Schrodinger wave equation is reduced by using classical method and in contrast to the usual controlling and pulse shaping methods of chemical reactions, the experimental data is not needed and this reduces the controlling costs.
NASA Astrophysics Data System (ADS)
Zhang, Jianzhong; Wang, Minxi; Cheng, Ming
2012-04-01
Iron losses in doubly salient permanent magnet (DSPM) machine are difficult to predict, as the flux waveforms are complex and dc bias existed. This paper measures iron losses at no load for different rotor speeds and these measured loss data are used to calibrate the iron loss model of the DSPM machine. Then the iron losses at rated load are predicted under three phase rectangular currents exerting on the armature windings. The result shows that small increment of iron losses is in the rotor at rated load which do benefit to the rotor thermal dissipation design.
Experimental study of cross flow mixing in cylindrical and rectangular ducts
NASA Technical Reports Server (NTRS)
Liscinsky, D. S.; Vranos, A.; Lohmann, R. P.
1993-01-01
An experimental investigation of non-reacting cross flow jet injection and mixing in cylindrical and rectangular ducts has been conducted with application to a low emissions combustor. Quantitative measurement of injectant concentration distributions perpendicular to the duct axis were obtained by planar digital imaging of the Mie-scattered light from an aerosol seed mixed with the injectant. The flowfield unmixedness was evaluated using (1) a mixing parameter derived from the ratio of the jet concentration fluctuations to the fully mixed concentration, and (2) probability density functions of the concentration distributions. Mixing rate was measured for 45 degree slant slot and round orifice injectors.
The calculation of the mass moment of inertia of a fluid in a rotating rectangular tank
NASA Technical Reports Server (NTRS)
1977-01-01
This analysis calculated the mass moment of inertia of a nonviscous fluid in a slowly rotating rectangular tank. Given the dimensions of the tank in the x, y, and z coordinates, the axis of rotation, the percentage of the tank occupied by the fluid, and angle of rotation, an algorithm was written that could calculate the mass moment of inertia of the fluid. While not included in this paper, the change in the mass moment of inertia of the fluid could then be used to calculate the force exerted by the fluid on the container wall.
Input impedance of coaxially fed rectangular microstrip antenna on electrically thick substrate
NASA Technical Reports Server (NTRS)
Chen, Wei; Lee, Kai-Fong; Lee, R. Q.
1993-01-01
A full-wave spectral domain analysis has been used to obtain input-impedance results for a probe-fed rectangular-patch antenna, modeling the source as a magnetic-current frill. Multiple modes are used in the probe surface current to account for axial and azimuthal variations. It is established that maximum resistance is dependent on the substrate loss tangent. The axial variation of the probe current must be taken into account for substrate thicknesses greater than about 0.02 wavelengths.
Photon exchange and entanglement formation during transmission through a rectangular quantum barrier
Sulyok, Georg; Durstberger-Rennhofer, Katharina; Summhammer, Johann
2015-01-01
When a quantum particle traverses a rectangular potential created by a quantum field both photon exchange and entanglement between particle and field take place. We present the full analytic solution of the Schrödinger equation of the composite particle–field system allowing investigation of these phenomena in detail and comparison to the results of a classical field treatment. Besides entanglement formation, remarkable differences also appear with respect to the symmetry between energy emission and absorption, resonance effects and if the field initially occupies the vacuum state. PMID:26345629
NASA Technical Reports Server (NTRS)
Siegel, R.
1993-01-01
An analytical solution was obtained by Siegel (1991, 1992) for local boundary heat fluxes by a radiating medium at uniform temperature in a 2D rectangular region. It is shown here that, after local fluxes from the medium to the walls have been evaluated, it is very easy to compute local fluxes arriving from the adjacent and opposite walls. This extends the previous analysis and provides convenient relations to include radiation from a black boundary, each side of the rectangle being at a different uniform temperature. The final expressions are helpful in performing spectral calculations that must be made for many spectral bands.
Mode-locked all-fiber laser producing radially polarized rectangular pulses.
Sun, Biao; Wang, Anting; Gu, Chun; Chen, Guoliang; Xu, Lixin; Chung, Dick; Zhan, Qiwen
2015-04-15
We propose and demonstrate a radially polarized mode-locked fiber laser through the use of a figure-8 cavity in combination with cascade fiber Bragg gratings (FBGs). The mode-locked laser emits rectangular pulses with width tunable from 2.8 to 23 ns under an increasing pump power at 1056.3 nm with 0.2-nm 30-dB linewidth. A polarization purity as high as 96% for the output transverse mode has been achieved simultaneously. PMID:25872049
Heat transfer studies on a rectangular channel with offset plate fins
NASA Astrophysics Data System (ADS)
Masterson, Jeffrey M.
1993-12-01
Convective heat transfer characteristics of a liquid cooled rectangular channel, containing offset plate fins, were investigated experimentally. The selected geometry was a 10x model of the fluid circulation passages in the commercially available SEM-E type electronic cooling modules. The test surface containing fins was made of aluminum and was heated at its base by a thermofoil heater. The Reynolds numbers were varied between 100-800, with water as the cooling fluid. Surface temperature measurements on the heated surface were used to determine the Colburn j factor. The effects of natural convection were also investigated.
NASA Astrophysics Data System (ADS)
Fertelli, Ahmet; Günhan, Gökhan; Buyruk, Ertan
2016-06-01
In the present study, it is aimed to calculate the effect of ice formation on different cylinder geometries placed in a rectangular cavity filled with water. For this aim Fluent package program was used to solve the flow domain numerically and temperature distribution and ice formation depending on time were illustrated. Water temperature in the cavity and cylinder surface temperature were assumed as 4, 8 and -10 °C respectively and firstly temperature distribution, velocity vector, liquid fraction and ratio of Ai/Ac (formed ice area/cross sectional area of cylinder) were determined for cylinders with different placement in fixed volume.
On the generation of secondary motion in circular to rectangular transition ducts
NASA Astrophysics Data System (ADS)
Demuren, A. O.
1993-01-01
A computer code has been developed for the calculation of three-dimensional turbulent flow in circular to rectangular transition ducts. The governing equations are written in a general curvilinear coordinate system so that all singly-connected geometrical configurations can be accommodated. Turbulence closure is through the standard k-epsilon model or a Reynolds stress closure model. Computed results show qualitative agreement with experimental data. Pressure-induced secondary flow is the dominant mode through the transition, but turbulence-induced secondary flow becomes prominent some distance downstream of the transition.
Theory of high-harmonic rectangular gyrotron for TE(mn) modes
NASA Technical Reports Server (NTRS)
Ferendeci, A. M.; Han, C. C.
1984-01-01
In this paper, the linearized relativistic Vlasov equation is solved and a dispersion relation is calculated for the interaction between a relativistic electron beam and the electromagnetic fields of a rectangular waveguide supporting TE(mn) modes. The dispersion relation is simplified to the special case of a frame of reference moving with the electrons and the resulting coupling coefficient epsilon(mn)super l is calculated for various TE(mn) modes. The dependence of epsilon(mn)super l on the parity of the harmonic number l and various mn modes of the waveguide are discussed.
Linear analysis of an axially grooved rectangular gyrotron for harmonic operation
NASA Technical Reports Server (NTRS)
Ferendeci, A. M.; Han, C. C.
1985-01-01
In an axially grooved rectangular waveguide the linearized Vlasov equation is solved to find the perturbed distribution function resulting from the electromagnetic forces on the electrons. The resulting beam current and the propagating electromagnetic waves of the cold tube are used in the inhomogeneous Maxwell's equation to derive the general dispersion equation. This equation is then transformed into the electron beam frame and the resulting linear growth rate of amplification is calculated. By maximizing the linear growth rate, the operational parameters of the gyrotron are then optimized.
NASA Astrophysics Data System (ADS)
Xiao, Junyan; Li, Zhe; Ye, Xiaozhou; Ma, Yurong; Qi, Limin
2013-12-01
Vertically aligned, supercrystalline microplates with a well-defined rectangular shape were fabricated in a large area through self-assembly of gold nanorods by a novel bulk solution evaporation method. This evaporative self-assembly strategy involving continuous movement of the contact line can prevent the coffee-ring effect, thus allowing uniform deposition of discrete GNR superstructures over a large area and favoring the formation of GNR supercrystals with geometrically symmetric shapes. A mechanism based on the continuing nucleation and growth of smectic GNR superstructures accompanying the movement of the contact line was put forward for the formation of the unique GNR supercrystal arrays. Based on this mechanism, a micropatterned substrate was designed to control the nucleation location and growth direction, leading to the spontaneous self-assembly of nearly parallel arrays of vertically aligned, supercrystalline microplates of GNRs. The obtained rectangular-plate-shaped GNR supercrystals exhibited interesting anisotropic optical reflection properties, which were revealed by polarized light microscopy.Vertically aligned, supercrystalline microplates with a well-defined rectangular shape were fabricated in a large area through self-assembly of gold nanorods by a novel bulk solution evaporation method. This evaporative self-assembly strategy involving continuous movement of the contact line can prevent the coffee-ring effect, thus allowing uniform deposition of discrete GNR superstructures over a large area and favoring the formation of GNR supercrystals with geometrically symmetric shapes. A mechanism based on the continuing nucleation and growth of smectic GNR superstructures accompanying the movement of the contact line was put forward for the formation of the unique GNR supercrystal arrays. Based on this mechanism, a micropatterned substrate was designed to control the nucleation location and growth direction, leading to the spontaneous self-assembly of
NASA Technical Reports Server (NTRS)
Wang, K. S.; Vaidya, P. G.
1975-01-01
The resonance expansion method, developed to study the propagation of sound in rigid rectangular ducts is applied to the case of slightly soft ducts. Expressions for the generation and decay of various harmonics are obtained. The effect of wall admittance is seen through a dissipation function in the system of nonlinear differential equations, governing the generation of harmonics. As the wall admittance increases, the resonance is reduced. For a given wall admittance this phenomenon is stronger at higher input intensities. Both the first and second order solutions are obtained and the results are extended to the case of ducts having mean flow.
Analytical solution for boundary heat fluxes from a radiating rectangular medium
NASA Technical Reports Server (NTRS)
Siegel, R.
1991-01-01
Reference is made to the work of Shah (1979) which demonstrated the possibility of partially integrating the radiative equations analytically to obtain an 'exact' solution. Shah's solution was given as a double integration of the modified Bessel function of order zero. Here, it is shown that the 'exact' solution for a rectangular region radiating to cold black walls can be conveniently derived, and expressed in simple form, by using an integral function, Sn, analogous to the exponential integral function appearing in plane-layer solutions.
Numerical Simulations of Noise Generated by Supersonic Rectangular Jets. Part One: Validation.
NASA Astrophysics Data System (ADS)
Viswanath, Kamal; Johnson, Ryan; Corrigan, Andrew; Kailasanath, Kazhikathra; Sanchez, Pablo; Baier, Florian; Gutmark, Ephraim
2015-11-01
The noise from high performance jet engines of both civilian and military aircraft is an area of active concern. To date, much of the work on noise reduction techniques has focused on axisymmetric circular nozzles. Asymmetric exhaust nozzle configurations, in particular rectangular, are likely to become more important in the future. In this study we validate the far field noise for ideally and over expanded supersonic jets issuing from a low aspect ratio rectangular nozzle geometry. Validation of the acoustic data is performed against experimentally recorded sound pressure level (SPL) spectra for a host of observer locations around the asymmetric nozzle. Data is presented for the cold jet case and two heated jets for all nozzle pressure ratios. It is shown that elevated operating temperatures result in elevated sound levels across the frequency spectra at all locations. Screech tones, that are present for certain cases, diminish in amplitude or cease completely as the jet is heated. Supported by Office of Naval Research (ONR) through the Computational Physics Task Area under the NRL 6.1 Base Program.
Numerical and experimental study of shock waves emanating from an open-ended rectangular tube
NASA Astrophysics Data System (ADS)
Koroteeva, E. Yu.; Znamenskaya, I. A.; Glazyrin, F. N.; Sysoev, N. N.
2016-04-01
We examine the dynamics of a high-speed shock-induced flow near the open end of a shock tube using the particle image velocimetry (PIV) and the background oriented schlieren (BOS) methods along with two- and three-dimensional numerical simulations. In experiments, planar shock waves (M=1.3 -1.6) are discharged from a rectangular (24 mm × 48 mm ) low-pressure section of a shock tube open to the atmosphere. Due to the rectangular exit geometry, the resulting flow is highly three-dimensional and, thus, more complicated, compared to well-studied circular/axisymmetric geometries. The study focuses on the spatio-temporal flow structure up to 1 ms after the shock wave diffraction. PIV and BOS visualization techniques share the same post-processing principle, and the iterative multi-step cross-correlation algorithm applied in the PIV software is adapted here for the calculation of background pattern displacement on the BOS images. Particular attention is given to the resolution of flow regions where sharp gradients are present, such as a diffracted shock front or embedded shocks. Computational fluid dynamic simulations of the problem are also conducted to validate the experimental results and methods and to gain more insight into the three-dimensional flow dynamics. PIV and BOS images are found to be consistent with the corresponding numerical flow visualizations.
Kiselev, V. A.; Linnik, A. F.; Onishchenko, I. N.; Onishchenko, N. I.; Sotnikov, G. V.; Uskov, V. V.; Marshall, T. C.
2006-11-27
A rectangular dielectric-lined metallic structure was studied that has an advantage over a cylindrical structure from the possibility of exciting by a sequence of bunches many equally-spaced modes, thereby building up a larger mode-locked wakefield. A rectangular vacuum copper waveguide was lined with two dielectric slabs, the size of which was calculated to provide resonant excitation of the fundamental LSM mode by a sequence of bunches with repetition frequency f0=2805 MHz, produced by linear resonant electron accelerator (4.5 MeV, number of bunches 6.103, diameter 1cm, duration 60 ps each, distance between bunches 300 ps, number of electrons in each bunch 109). The waveguide has cross section 85 mm x 180 mm, and Teflon ({epsilon} 2.1) plates were placed along the smaller sides of the waveguide, their thickness from the calculation being 22 mm. In experiments, the length of the resonator was 535mm. We found that the total wakefield is three times larger than the fundamental mode; thus a greater number of excited modes was excited compared with the cylindrical case, for which this ratio was only 1.5. We found considerably more energy loss of electron bunches for the resonator case compared with the waveguide case.
NASA Astrophysics Data System (ADS)
Yang, Ziqiang; Yang, Tao; Liu, Yu; Peng, Hao
2016-02-01
In this paper, a compact full Ka-band differential microstrip line (DML) to rectangular waveguide transition is proposed. The dipole antenna with semi-elliptic arms is introduced to transform the differential mode of DML to the TE10 mode of the rectangular waveguide directly. The two arms of the dipole antenna are connected together by a shorting strip to reduce the size of the dipole. Compared with the DML-to-waveguide transition using the fin-line topology, the size of the proposed transition has been reduced by 86 %. To verify this transition, a back-to-back structure is fabricated and tested. It provides a return loss of better than 15.2 dB and an insertion loss of 0.73 to 1.07 dB within a wide frequency range from 26.5 to 40 GHz. The measurement results show good agreement with the simulation results. Furthermore, a tolerance analysis is also performed via the simulation to prove that this transition is robust in the fabrication and mechanical assembly.
Mixing characteristics of a moderate aspect ratio screeching supersonic rectangular jet
NASA Astrophysics Data System (ADS)
Valentich, Griffin; Upadhyay, Puja; Kumar, Rajan
2016-05-01
Flow field characteristics of a moderate aspect ratio supersonic rectangular jet were examined at two overexpanded, a perfectly expanded, and an underexpanded jet conditions. The underexpanded and one overexpanded operating condition were of maximum screech, while the second overexpanded condition was of minimum screech intensity. Streamwise particle image velocimetry was performed along both major and minor axes of the jet and the measurements were made up to 30 nozzle heights, h, where h is the small dimension of the nozzle. Select cross planes were examined using stereoscopic particle image velocimetry to investigate the jet development and the role streamwise vortices play in jet spreading at each operating condition. The results show that streamwise vortices present at the nozzle corners along with vortices excited by screech tones play a major role in the jet evolution. All cases except for the perfectly expanded operating condition exhibited axis switching at streamwise locations ranging from 11 to 16 nozzle heights downstream of the exit. The overexpanded condition of maximum screech showed the most upstream switch over, while the underexpanded case showed the farthest downstream. Both of the maximum screeching cases developed into a diamond cross-sectional profile far downstream of the exit, while the ideally expanded case maintained a rectangular shape. The overexpanded minimum screeching case eventually decayed into an oblong profile.
Ansari, Mohd Zahid; Cho, Chongdu
2009-01-01
This study presents the deflection, resonant frequency and stress results of rectangular, triangular, and step profile microcantilevers subject to surface stress. These cantilevers can be used as the sensing element in microcantilever biosensors. To increase the overall sensitivity of microcantilever biosensors, both the deflection and the resonant frequency of the cantilever should be increased. The effect of the cantilever profile change and the cantilever cross-section shape change is first investigated separately and then together. A finite element code ANSYS Multiphysics is used and solid finite elements cantilever models are solved. A surface stress of 0.05 N/m was applied to the top surface of the cantilevers. The cantilevers are made of silicon with elastic modulus 130 GPa and Poisson’s ratio 0.28. To show the conformity of this study, the numerical results are compared against their analytical ones. Results show that triangular and step cantilevers have better deflection and frequency characteristics than rectangular ones. PMID:22454571
Li, Rui; Ye, Hongfei; Zhang, Weisheng; Ma, Guojun; Su, Yewang
2015-01-01
Spring constant calibration of the atomic force microscope (AFM) cantilever is of fundamental importance for quantifying the force between the AFM cantilever tip and the sample. The calibration within the framework of thin plate theory undoubtedly has a higher accuracy and broader scope than that within the well-established beam theory. However, thin plate theory-based accurate analytic determination of the constant has been perceived as an extremely difficult issue. In this paper, we implement the thin plate theory-based analytic modeling for the static behavior of rectangular AFM cantilevers, which reveals that the three-dimensional effect and Poisson effect play important roles in accurate determination of the spring constants. A quantitative scaling law is found that the normalized spring constant depends only on the Poisson’s ratio, normalized dimension and normalized load coordinate. Both the literature and our refined finite element model validate the present results. The developed model is expected to serve as the benchmark for accurate calibration of rectangular AFM cantilevers. PMID:26510769
NASA Astrophysics Data System (ADS)
Ma, Chien-Ching; Lin, Hsien-Yang
2005-09-01
This study provides two non-contact optical techniques to investigate the transverse vibration characteristics of piezoceramic rectangular plates in resonance. These methods, including the amplitude-fluctuation electronic speckle pattern interferometry (AF-ESPI) and laser Doppler vibrometer (LDV), are full-field measurement for AF-ESPI and point-wise displacement measurement for LDV, respectively. The edges of these piezoceramic rectangular plates may either be fixed or free. Both resonant frequencies and mode shapes of vibrating piezoceramic plates can be obtained simultaneously by AF-ESPI. Excellent quality of the interferometric fringe patterns for the mode shapes is obtained. In the LDV system, a built-in dynamic signal analyzer (DSA) composed of DSA software and a plug-in waveform generator board can provide the piezoceramic plates with the swept-sine excitation signal, whose gain at corresponding frequencies is analyzed by the DSA software. The peaks appeared in the frequency response curve are resonant frequencies. In addition to these optical methods, the numerical computation based on the finite element analysis is used to verify the experimental results. Good agreements of the mode shapes and resonant frequencies are obtained for experimental and numerical results.
NASA Astrophysics Data System (ADS)
Cupiał, Piotr
2015-09-01
The paper discusses a perturbation solution of the natural frequencies and mode shapes of a piezoelectric rectangular plate modelled as a three-dimensional body. The coupled theory of piezoelectricity is used, with the governing equations consisting of one electrostatic and three mechanical equations coupled through the piezoelectric effect. Analytical perturbation formulas up to the first-order terms have been derived and used. An important difference of the present analysis as compared to the classical perturbation method consists in that the small parameter enters not only the governing equations but the boundary conditions as well. To address this complication an efficient new approach that makes use of generalized functions has been proposed. Results of the natural frequencies and mode shapes obtained by the perturbation method are discussed for a thin piezoelectric rectangular plate, a thick plate and a piezoelectric parallelepiped. All the results obtained using the perturbation method have been compared with the exact solutions of the coupled electromechanical problem. The proposed perturbation approach furnishes an efficient approximate method of studying the coupled piezoelectric vibration problem. The main advantage of the method derives from the fact that only the elastic solution is required, the effect of piezoelectric coupling being accounted for at a post-processing stage.
Venkatesham, B; Tiwari, Mayank; Munjal, M L
2010-10-01
This paper describes an analytical calculation of break-out noise from a rectangular plenum with four flexible walls by incorporating three-dimensional effects along with the acoustical and structural wave coupling phenomena. The breakout noise from rectangular plenums is important and the coupling between acoustic waves within the plenum and structural waves in the flexible plenum walls plays a critical role in prediction of the transverse transmission loss. The first step in breakout noise prediction is to calculate the inside plenum pressure field and the normal flexible plenum wall vibration by using an impedance-mobility approach, which results in a compact matrix formulation. In the impedance-mobility compact matrix (IMCM) approach, it is presumed that the coupled response can be described in terms of finite sets of the uncoupled acoustic subsystem and the structural subsystem. The flexible walls of the plenum are modeled as an unfolded plate to calculate natural frequencies and mode shapes of the uncoupled structural subsystem. The second step is to calculate the radiated sound power from the flexible walls using Kirchhoff-Helmholtz (KH) integral formulation. Analytical results are validated with finite element and boundary element (FEM-BEM) numerical models. PMID:20968352
Enhanced mixing of a rectangular supersonic jet by natural and induced screech
NASA Technical Reports Server (NTRS)
Rice, Edward J.; Raman, Ganesh
1993-01-01
The influence of shear layer excitation on the mixing of supersonic rectangular jets was studied experimentally. Two methods of excitation were used to control the jet mixing. The first used the natural screech of an underexpanded supersonic jet from a converging nozzle. The level of the screech excitation was controlled by the use of a pair of baffles located to block the acoustic feedback path between the downstream shock structure and the nozzle lip. A screech level variation of over 30 decibels was achieved and the mixing was completely determined by the level of screech attained at the nozzle lip. The second form of self-excitation used the induced screech caused by obstacles or paddles located in the shear layers on either long side of the rectangular jet. With sufficient immersion of the paddles intense jet mixing occurred and large flapping wave motion was observed using a strobed focused Schlieren system. Each paddle was instrumented with a total pressure tap and strain gages to determine the pressure and drag force on the square cross-section paddle. Considerable drag was observed in this initial exploratory study. Future studies using alternate paddle geometries will be conducted to maximize jet mixing with minimum drag.
Patterning square and rectangular arrays using shear-aligned block copolymer thin films
NASA Astrophysics Data System (ADS)
Kim, So Youn; Davis, Raleigh L.; Register, Richard A.; Gwyther, Jessica; Nunns, Adam; Manners, Ian; Chaikin, Paul M.
2014-03-01
Microphase separation of block copolymers in thin films can generate periodic structures: hexagonally packed arrays of dots from spherical or cylindrical phase block copolymers, or periodic stripes from cylindrical or lamellar phase block copolymers. Square or rectangular patterns, however, do not naturally form by spontaneous self-assembly of a simple diblock copolymer, and are a challenge to create. We present a simple way to create nano-square/rectangular arrays by building up a double-layer film of a cylinder-forming diblock, where each layer is sequentially deposited, shear-aligned independently, and cross-linked. Any block copolymer with at least one crosslinkable block can in principle be employed; in this study we use cylinder-forming polystyrene-b-poly(ferrocenylisopropylmethylsilane) and polystyrene-b-poly(hexylmethacrylate). The pitch of the array is tunable by varying polymer molecular weight. Oxygen reactive ion etching is used to reveal the grid structures, and these grids can in turn form nano-wells in the silicon substrate when the cylinder-forming block is very etch-resistant under the conditions used for silicon etching. Additionally, metal dots ordered in square arrays can be created using these grids as templates, via metal evaporation and lift-off.
Weak commutation relations and eigenvalue statistics for products of rectangular random matrices.
Ipsen, Jesper R; Kieburg, Mario
2014-03-01
We study the joint probability density of the eigenvalues of a product of rectangular real, complex, or quaternion random matrices in a unified way. The random matrices are distributed according to arbitrary probability densities, whose only restriction is the invariance under left and right multiplication by orthogonal, unitary, or unitary symplectic matrices, respectively. We show that a product of rectangular matrices is statistically equivalent to a product of square matrices. Hereby we prove a weak commutation relation of the random matrices at finite matrix sizes, which previously has been discussed for infinite matrix size. Moreover, we derive the joint probability densities of the eigenvalues. To illustrate our results, we apply them to a product of random matrices drawn from Ginibre ensembles and Jacobi ensembles as well as a mixed version thereof. For these weights, we show that the product of complex random matrices yields a determinantal point process, while the real and quaternion matrix ensembles correspond to Pfaffian point processes. Our results are visualized by numerical simulations. Furthermore, we present an application to a transport on a closed, disordered chain coupled to a particle bath. PMID:24730789
Minimum weight design of rectangular and tapered helicopter rotor blades with frequency constraints
NASA Technical Reports Server (NTRS)
Chattopadhyay, Aditi; Walsh, Joanne L.
1988-01-01
The minimum weight design of a helicopter rotor blade subject to constraints on coupled flap-lag natural frequencies has been studied. A constraint has also been imposed on the minimum value of the autorotational inertia of the blade in order to ensure that it has sufficient inertia to autorotate in the case of engine failure. The program CAMRAD is used for the blade modal analysis and CONMIN is used for the optimization. In addition, a linear approximation analysis involving Taylor series expansion has been used to reduce the analysis effort. The procedure contains a sensitivity analysis which consists of analytical derivatives of the objective function and the autorotational inertia constraint and central finite difference derivatives of the frequency constraints. Optimum designs have been obtained for both rectangular and tapered blades. Design variables include taper ratio, segment weights, and box beam dimensions. It is shown that even when starting with an acceptable baseline design, a significant amount of weight reduction is possible while satisfying all the constraints for both rectangular and tapered blades.
Hilbert transform and exponential integral estimates of rectangular sums of double Fourier series
NASA Astrophysics Data System (ADS)
Karagulyan, G. A.
1996-04-01
A new integral estimate for rectangular partial sums of double Fourier series is obtained. The main result of the paper is the following.Theorem. For any f\\in L\\log L(\\mathbf T^2) and \\delta>0 there exists a set E_{\\delta,f}\\in\\mathbf T^2, \\vert E_{\\delta,f}\\vert>(2\\pi)^2-\\delta such that \\displaystyle 1)\\quad\\int_{E_{\\delta,f}}\\exp\\biggl\\lbrack\\frac{c_1\\delta\\vert ......L(\\mathbf T^2)}}\\biggr\\rbrack^{1/2}\\,dx\\,dy\\leqslant C_2, \\qquad N,M=1,2,\\dots, \\displaystyle 2)\\quad\\lim_{N,M\\to\\infty}\\int_{E_{\\delta,f}}\\bigl\\lbrack\\exp(\\vert S_{N,M}(x,y,f)-f(x,y)\\vert)^{1/2}-1\\bigr\\rbrack\\,dx\\,dy=0. This theorem yields estimates almost everywhere for rectangular sums of double Fourier series and convergence in L^p on sets of large measure.
Lee, Yuna; Park, Yeong-Shin; Jo, Jong-Gab; Yang, J J; Hwang, Y S
2012-02-01
Microwave plasma ion source with rectangular cavity resonator has been examined to improve ion beam current by changing wave launcher type from single-port to double-port. The cavity resonators with double-port and single-port wave launchers are designed to get resonance effect at TE-103 mode and TE-102 mode, respectively. In order to confirm that the cavities are acting as resonator, the microwave power for breakdown is measured and compared with the E-field strength estimated from the HFSS (High Frequency Structure Simulator) simulation. Langmuir probe measurements show that double-port cavity enhances central density of plasma ion source by modifying non-uniform plasma density profile of the single-port cavity. Correspondingly, beam current from the plasma ion source utilizing the double-port resonator is measured to be higher than that utilizing single-port resonator. Moreover, the enhancement in plasma density and ion beam current utilizing the double-port resonator is more pronounced as higher microwave power applied to the plasma ion source. Therefore, the rectangular cavity resonator utilizing the double-port is expected to enhance the performance of plasma ion source in terms of ion beam extraction. PMID:22380295
Lee, Yuna; Park, Yeong-Shin; Jo, Jong-Gab; Yang, J. J.; Hwang, Y. S.
2012-02-15
Microwave plasma ion source with rectangular cavity resonator has been examined to improve ion beam current by changing wave launcher type from single-port to double-port. The cavity resonators with double-port and single-port wave launchers are designed to get resonance effect at TE-103 mode and TE-102 mode, respectively. In order to confirm that the cavities are acting as resonator, the microwave power for breakdown is measured and compared with the E-field strength estimated from the HFSS (High Frequency Structure Simulator) simulation. Langmuir probe measurements show that double-port cavity enhances central density of plasma ion source by modifying non-uniform plasma density profile of the single-port cavity. Correspondingly, beam current from the plasma ion source utilizing the double-port resonator is measured to be higher than that utilizing single-port resonator. Moreover, the enhancement in plasma density and ion beam current utilizing the double-port resonator is more pronounced as higher microwave power applied to the plasma ion source. Therefore, the rectangular cavity resonator utilizing the double-port is expected to enhance the performance of plasma ion source in terms of ion beam extraction.
Wei, Wei; Yi, Lilin; Jaouën, Yves; Hu, Weisheng
2014-09-22
We propose a rectangular optical filter based on stimulated Brillouin scattering (SBS) in optical fiber with bandwidth tuning from 50 MHz to 4 GHz at less than 15-MHz resolution. The rectangular shape of the filter is precisely achieved utilizing digital feedback control of the comb-like pump spectral lines. The passband ripple is suppressed to ~1 dB by mitigating the nonlinearity influences of the comb-like pump lines generated in electrical and optical components and fibers. Moreover a fiber with a single Brillouin peak is employed to further reduce the in-band ripple and the out-of-band SBS gain at the same time. Finally, we analyze the noise performance of the filter at different bandwidth cases and demonstrate the system performance of the proposed filter with 2.1-GHz bandwidth and 19-dB gain by amplifying a 2-GHz orthogonal frequency-division-multiplexing (OFDM) signal with quadrature-phase-shift-keying (QPSK) and 16-quadrature-amplitude-modulation (16-QAM) on each subscriber. PMID:25321794
NASA Astrophysics Data System (ADS)
Yamamoto, Takehiro; Yamasaki, Yasuo; Tanaka, Yusuke; Mori, Noriyasu
2006-07-01
Three-dimensional flows of liquid crystalline polymers (LCPs) in a rectangular 3 to 1 abrupt contraction channel and a rectangular 1 to 3 abrupt expansion channel are numerically analyzed to investigate the molecular orientation behavior of LCPs in complex flows. A modified Doi model is used as a constitutive equation and MAC (marker and cell)-based finite difference method is employed for the numerical technique for solving the basic equations. In the contraction flow, most molecules are aligned in the flow direction near the contraction owing to elongational flow except for a vortex region. Just downstream of the contraction, the velocity overshoot occurs owing to the molecular orientation near the contraction. In the expansion flow, on the other hand, molecules near the mid-plane are aligned perpendicular to the flow direction just downstream of the expansion. This alignment is related to a concave velocity profile appeared in this region. Moreover, the decelerating flow downstream of the expansion causes a three-dimensional structure of directors called a twist structure.
Measurement of heat transfer and pressure drop in rectangular channels with turbulence promoters
NASA Technical Reports Server (NTRS)
Han, J. C.; Park, J. S.; Ibrahim, M. Y.
1986-01-01
Periodic rib turbulators were used in advanced turbine cooling designs to enhance the internal heat transfer. The objective of the present project was to investigate the combined effects of the rib angle of attack and the channel aspect ratio on the local heat transfer and pressure drop in rectangular channels with two opposite ribbed walls for Reynolds number varied from 10,000 to 60,000. The channel aspect ratio (W/H) was varied from 1 to 2 to 4. The rib angle of attack (alpha) was varied from 90 to 60 to 45 to 30 degree. The highly detailed heat transfer coefficient distribution on both the smooth side and the ribbed side walls from the channel sharp entrance to the downstream region were measured. The results showed that, in the square channel, the heat transfer for the slant ribs (alpha = 30 -45 deg) was about 30% higher that of the transverse ribs (alpha = 90 deg) for a constant pumping power. However, in the rectangular channels (W/H = 2 and 4, ribs on W side), the heat transfer at alpha = 30 -45 deg was only about 5% higher than 90 deg. The average heat transfer and friction correlations were developed to account for rib spacing, rib angle, and channel aspect ratio over the range of roughness Reynolds number.
NASA Technical Reports Server (NTRS)
Miller, Steven A.; Morris, Philip J.
2010-01-01
Supersonic jets operating off-design produce broadband shock-associated noise. Broadband shock-associated noise is characterized by multiple broadband peaks in the far-field and is often the dominant source of noise towards the sideline and upstream direction relative to the jet axis. It is due to large scale coherent turbulence structures in the jet shear layers interacting with the shock cell structure. A broadband shock-associated noise model recently developed by the authors predicts this noise component from solutions to the Reynolds averaged Navier-Stokes equations using a two-equation turbulence model. The broadband shock-associated noise model is applied to dualstream and rectangular nozzles operating supersonically, heated, and off-design. The dualstream jet broadband shock-associated noise predictions are conducted for cases when the core jet is supersonic and the fan jet is subsonic, the core jet is subsonic and the fan jet is supersonic, and when both jet streams operate supersonically. Rectangular jet predictions are shown for a convergent-divergent nozzle operating both over- and under-expanded for cold and heated conditions. The original model implementation has been heavily modified to make accurate predictions for the dualstream jets. It is also argued that for over-expanded jets the oblique shock wave attached to the nozzle lip contributes little to broadband shock-associated noise. All predictions are compared with experiments.
Li, Rui; Ye, Hongfei; Zhang, Weisheng; Ma, Guojun; Su, Yewang
2015-01-01
Spring constant calibration of the atomic force microscope (AFM) cantilever is of fundamental importance for quantifying the force between the AFM cantilever tip and the sample. The calibration within the framework of thin plate theory undoubtedly has a higher accuracy and broader scope than that within the well-established beam theory. However, thin plate theory-based accurate analytic determination of the constant has been perceived as an extremely difficult issue. In this paper, we implement the thin plate theory-based analytic modeling for the static behavior of rectangular AFM cantilevers, which reveals that the three-dimensional effect and Poisson effect play important roles in accurate determination of the spring constants. A quantitative scaling law is found that the normalized spring constant depends only on the Poisson's ratio, normalized dimension and normalized load coordinate. Both the literature and our refined finite element model validate the present results. The developed model is expected to serve as the benchmark for accurate calibration of rectangular AFM cantilevers. PMID:26510769
Note: compact helical pulse forming line for the generation of longer duration rectangular pulse.
Sharma, Surender Kumar; Deb, P; Sharma, Archana; Shukla, R; Prabaharan, T; Adhikary, B; Shyam, A
2012-06-01
The helical pulsed forming line (PFL) can generate longer duration rectangular pulse in a smaller length. A compact PFL using helical water line is designed and experimentally investigated. The impedance of the helical PFL is 22 [ohm sign]. The compactness is achieved in terms of reduction in length of the PFL by a factor of 5.5 using helical water PFL as compared to coaxial water PFL of same length. The helical PFL was pulsed charged to 200 kV using a high voltage pulse transformer in 4.5 μs and discharged into the matched 22 Ω resistive load through a self-breakdown pressurized spark gap switch. The rectangular voltage pulse of 100 kV, 260 ns (FWHM) is measured across the load. The effect of reduction in water temperature on the pulse width is also studied experimentally. The increase in pulse width up to 7% more is observed by reducing the temperature of the deionized water to 5 °C. It will further reduce the length of the PFL and make the system small for compact pulsed power drivers. PMID:22755669
NASA Astrophysics Data System (ADS)
Li, Rui; Ye, Hongfei; Zhang, Weisheng; Ma, Guojun; Su, Yewang
2015-10-01
Spring constant calibration of the atomic force microscope (AFM) cantilever is of fundamental importance for quantifying the force between the AFM cantilever tip and the sample. The calibration within the framework of thin plate theory undoubtedly has a higher accuracy and broader scope than that within the well-established beam theory. However, thin plate theory-based accurate analytic determination of the constant has been perceived as an extremely difficult issue. In this paper, we implement the thin plate theory-based analytic modeling for the static behavior of rectangular AFM cantilevers, which reveals that the three-dimensional effect and Poisson effect play important roles in accurate determination of the spring constants. A quantitative scaling law is found that the normalized spring constant depends only on the Poisson’s ratio, normalized dimension and normalized load coordinate. Both the literature and our refined finite element model validate the present results. The developed model is expected to serve as the benchmark for accurate calibration of rectangular AFM cantilevers.
Mixing noise reduction for rectangular supersonic jets by nozzle shaping and induced screech mixing
NASA Technical Reports Server (NTRS)
Rice, Edward J.; Raman, Ganesh
1993-01-01
Two methods of mixing noise modification were studied for supersonic jets flowing from rectangular nozzles with an aspect ratio of about five and a small dimension of about 1.4 cm. The first involves nozzle geometry variation using either single (unsymmetrical) or double bevelled (symmetrical) thirty degree cutbacks of the nozzle exit. Both converging (C) and converging-diverging (C-D) versions were tested. The double bevelled C-D nozzle produced a jet mixing noise reduction of about 4 dB compared to a standard rectangular C-D nozzle. In addition all bevelled nozzles produced an upstream shift in peak mixing noise which is conducive to improved attenuation when the nozzle is used in an acoustically treated duct. A large increase in high frequency noise also occurred near the plane of the nozzle exit. Because of near normal incidence, this noise can be easily attenuated with wall treatment. The second approach uses paddles inserted on the edge of the two sides of the jet to induce screech and greatly enhance the jet mixing. Although screech and mixing noise levels are increased, the enhanced mixing moves the source locations upstream and may make an enclosed system more amenable to noise reduction using wall acoustic treatment.
Twin Jet Effects on Noise of Round and Rectangular Jets: Experiment and Model
NASA Technical Reports Server (NTRS)
Bozak, Rick
2014-01-01
Many subsonic and supersonic aircraft concepts proposed by NASA's Fundamental Aeronautics Program have asymmetric, integrated propulsion systems. The asymmetries in the exhaust of these propulsion systems create an asymmetric acoustic field. The asymmetries investigated in the current study are from twin jets and rectangular nozzles. Each effect produces its own variation of the acoustic field. An empirical model was developed to predict the acoustic field variation from round twin jets with twin jet spacing from 2.6 to 5.6, where s is the center-to-center spacing over the jet diameter. The model includes parameters to account for the effects of twin jet spacing, jet static temperature ratio, flight Mach number, frequency, and observer angle (both polar and azimuthal angles). The model was then applied to twin 2:1 and 8:1 aspect ratio nozzles to determine the impact of jet aspect ratio. For the round and rectangular jets, the use of the model reduces the average magnitude of the error over all frequencies, observation angles, and jet spacings by approximately 0.5dB when compared against the assumption of adding two jets incoherently.
NASA Technical Reports Server (NTRS)
Miles, Jeffrey Hilton
1999-01-01
A linear spatial instability model for multiple spatially periodic supersonic rectangular jets is solved using Floquet-Bloch theory. It is assumed that in the region of interest a coherent wave can propagate. For the case studied large spatial growth rates are found. This work is motivated by an increase in mixing found in experimental measurements of spatially periodic supersonic rectangular jets with phase-locked screech and edge tone feedback locked subsonic jets. The results obtained in this paper suggests that phase-locked screech or edge tones may produce correlated spatially periodic jet flow downstream of the nozzles which creates a large span wise multi-nozzle region where a coherent wave can propagate. The large spatial growth rates for eddies obtained by model calculation herein are related to the increased mixing since eddies are the primary mechanism that transfer energy from the mean flow to the large turbulent structures. Calculations of spacial growth rates will be presented for a set of relative Mach numbers and spacings for which experimental measurements have been made. Calculations of spatial growth rates are presented for relative Mach numbers from 1.25 to 1.75 with ratios of nozzle spacing to nozzle width ratios from s/w(sub N) = 4 to s/w(sub N) = 13.7. The model may be of significant scientific and engineering value in the quest to understand and construct supersonic mixer-ejector nozzles which provide increased mixing and reduced noise.
Mixed convection heat and mass transfer in radially rotating rectangular ducts
Lee, K.T.; Yan, W.M.
1998-11-27
Heat transfer in rotating ducts is encountered in many engineering applications, such as cooling of turbomachinery, gas turbines, and other rotating systems. The present work investigates mixed convection heat and mass transfer in the entrance region of radially rotating rectangular ducts with water film evaporation along the porous duct walls. Mechanisms of secondary vortex development in the ducts under various conditions are examined by a vorticity-velocity numerical method. Emphasis is placed on the rotation effects, including both Coriolis and centrifugal buoyancy forces, and the mass diffusion effect on the flow structure and heat transfer characteristics. Results are presented in particular for an air-water vapor system under various conditions. Predicted results show that the effects of liquid film evaporation along the porous duct walls on the mixed convection heat transfer are rather substantial. The magnitude of the evaporative latent heat transfer may be 10 times greater than that of sensible heat transfer. The predictions also demonstrate that the distributions of Nu, Sh{sub z}, and fRe are closely related to the emergence, disappearance, growth, and decay of the rotating-induced secondary vortices. Additionally, a higher Nu{sub z} is found for a rectangular duct with a larger aspect ratio ({gamma} = 2) due to the relatively stronger secondary flows.
Capillary flow enhancement in rectangular polymer microchannels with a deformable wall
NASA Astrophysics Data System (ADS)
Anoop, R.; Sen, A. K.
2015-07-01
We report the capillary flow enhancement in rectangular polymer microchannels, when one of the channel walls is a deformable polymer membrane. We provide detailed insight into the physics of elastocapillary interaction between the capillary flow and elastic membrane, which leads to significant improvements in capillary flow performance. As liquid flows by capillary action in such channels, the deformable wall deflects inwards due to the Young-Laplace pressure drop across the liquid meniscus. This, in turn, decreases the radius of curvature of the meniscus and increases the driving capillary pressure. A theoretical model is proposed to predict the resultant increase in filling speed and rise height, respectively, in deformable horizontal and vertical microchannels having large aspect ratios. A non-dimensional parameter J , which represents the ratio of the capillary force to the mechanical restoring force, is identified to quantify the elastocapillary effects in terms of the improvement in filling speed (for J >0.238 ) and the condition for channel collapse (J >1 ). The theoretical predictions show good agreement with experimental data obtained using deformable rectangular poly(dimethylsiloxane) microchannels. Both model predictions and experimental data show that over 15% improvement in the Washburn coefficient in horizontal channels, and over 30% improvement in capillary rise height in vertical channels, are possible prior to channel collapse. The proposed technique of using deformable membranes as channel walls is a viable method for capillary flow enhancement in microfluidic devices.
NASA Astrophysics Data System (ADS)
Amabili, M.; Farhadi, S.
2009-02-01
In the present study, (i) the classical Von Kárman theory, (ii) the first-order shear deformation theory and (iii) the higher-order (third-order) shear deformation theory are compared for studying the nonlinear forced vibrations of isotropic and laminate composite rectangular plates. In particular, the harmonic response in the frequency neighborhood of the fundamental mode of rectangular plates is investigated and the response curves computed by using the three different theories are compared. The boundary conditions of the plates are simply supported with immovable edges. Geometric imperfections are taken into account. Calculations for isotropic and laminated composite plates are presented and results are discussed. For isotropic plates, the frequency-response curves for large-amplitude vibrations obtained by using the three theories are almost coincident. For laminated composite plates, differences arise for relatively thick plates (ratio between the thickness and the edge equal to 0.1), while for thin plates (ratio between the thickness and the edge equal to 0.01), no difference is obtained. For all cases, the first-order shear deformation (with shear correction factor √{3}/2) and the higher-order shear deformation theories give practically coincident results and differences are observed with respect to the classical Von Kárman theory.
BUCKO- A BUCKLING ANALYSIS FOR RECTANGULAR PLATES WITH CENTRALLY LOCATED CUTOUTS
NASA Technical Reports Server (NTRS)
Nemeth, M. P.
1994-01-01
BUCKO is a computer program developed to predict the buckling load of a rectangular compression-loaded orthotropic plate with a centrally located cutout. The plate is assumed to be a balanced, symmetric laminate of uniform thickness. The cutout shape can be elliptical, circular, rectangular, or square. The BUCKO package includes sample data that demonstrates the essence of the program and its ease of usage. BUCKO uses an approximate one-dimensional formulation of the classical two-dimensional buckling problem following the Kantorovich method. The boundary conditions are considered to be simply supported unloaded edges and either clamped or simply supported loaded edges. The plate is loaded in uniaxial compression by either uniformly displacing or uniformly stressing two opposite edges of the plate. The BUCKO analysis consists of two parts: calculation of the inplane stress distribution prior to buckling, and calculation of the plate axial load and displacement at buckling. User input includes plate planform and cutout geometry, plate membrane and bending stiffnesses, finite difference parameters, boundary condition data, and loading data. Results generated by BUCKO are the prebuckling strain energy, inplane stress resultants, buckling mode shape, critical end shortening, and average axial and transverse strains at buckling. BUCKO is written in FORTRAN V for batch execution and has been implemented on a CDC CYBER 170 series computer operating under NOS with a central memory requirement of approximately 343K of 60 bit words. This program was developed in 1984 and was last updated in 1990.
Asako, Y. . Dept. of Mechanical Engineering); Faghri, M. . Dept. of Mechanical Engineering); Charmchi, M. . Dept. of Mechanical Engineering); Bahrami, P.A. )
1994-02-01
An enthalpy method is employed to solve transport processes associated with melting of an unfixed rectangular phase change material (PCM) in a low-gravitational environment. This method permits the phase-change problems to be solved within fixed numerical grids, hence eliminating the need for coordinate transformation. The PCM, initially at its melting temperature, is placed inside a rectangular enclosure. The lower surface of the container is then exposed to a uniform temperature higher than the PCM melting temperature. The difference in densities of solid and liquid causes a force imbalance on the solid phase exceeds that of the liquid, the solid continually moves downward as melting progresses and hence generates a flow field within the liquid. The problem is formulated as a one-domain problem with the possibility of melting from all the PCM surfaces, and no approximation is made about the liquid film thickness under the melt. The governing equations are discretized by using a control-volume-based finite difference scheme with a new iterative method to correct for the downward solid-phase velocity. This will also speed up the convergence of the numerical procedure. The results are presented in the form of a parametric study of the effects of Archimedes number, Stefan number, Prandtl number, and the geometric parameters on the melt thickness, the downward solid velocity, the elevation of the top surface, and the volume of the solid PCM. They show that in a low-gravitational environment, the melting rate is very slow.
Cold test, spontaneous emission and gain in a rectangular Cerenkov amplifier
Scharer, J.E.; Joe, J.; Booske, J.H.; Basten, M.; Kirolous, H.
1994-12-31
The authors present experimental results for the rectangular Cerenkov grating amplifier. This research is being carried out to develop a Ka-band (35 GHz), low voltage (10 kV), moderate power (10 kW) source. They have constructed a Ku-band grating structure to study a scaled version of this source. The tapered grating consists of two tapered Ku-band smooth wave guide sections and two 3.5-inch sections of five-step-tapered gratings. Both tapered and untapered grating structures have been cold tested utilizing the network analyzer measurements. They find that their taper design reduced the reflection coefficient from {minus}5 dB to less than {minus}20 dB over a 12--15 GHz bandwidth. Spontaneous emission results resulting from passing the circular electron beam from a Litton thermionic gun over the grating structure will be presented. They have theoretically investigated the sheet beam interaction with hybrid modes in a deep groove rectangular grating waveguide. A complex dispersion relation, which includes a finite axial energy spread of the beam, describing the interaction has been solved. The authors find that the instability is always convective in the forward wave mode regime.
Finite Element Analysis on Warm Hydroforming of Rectangular Mg Alloy Cups with a Step Cavity
Zhang Shihong; Zheng Wentao; Xu Yongchao; Wang Zhongtang
2005-08-05
Magnesium alloys, as one of the lightest metal structural materials, are attracting more and more attention. At present, most of Mg alloy products are manufactured by die casting. For enlarging the applications of Mg alloys, many researchers are engaged in developing its plastic forming technology. However, the study on warm sheet hydroforming of Mg alloy is rarely reported. Therefore, a set of warm sheet hydroforming tools was designed for experimental research on the hydroforming of rectangular Mg alloy cups with a step cavity. The corners of the deeper cavity are difficult to form directly because of the severe stretching. Multi-stage hydroforming method was used to improve the sheet thickness reduction in the corners of the deeper cavity. Several different two-stage hydroforming methods were realized by elastic-plastic finite element simulation. According to the results of finite element simulation, the influence of forming methods on the minimum thickness of formed parts and the reasons were analyzed, and the optimal process for the rectangular Mg alloy cup with a step cavity was determined.
Broadband attenuation of Lamb waves through a periodic array of thin rectangular junctions
NASA Astrophysics Data System (ADS)
Moiseyenko, Rayisa P.; Pennec, Yan; Marchal, Rémi; Bonello, Bernard; Djafari-Rouhani, Bahram
2014-10-01
We study theoretically subwavelength physical phenomena, such as resonant transmission and broadband sound shielding for Lamb waves propagating in an acoustic metamaterial made of a thin plate drilled with one or two row(s) of rectangular holes. The resonances and antiresonances of periodically arranged rectangular junctions separated by holes are investigated as a function of the geometrical parameters of the junctions. With one and two row(s) of holes, high frequency specific features in the transmission coefficient are explained in terms of a coupling of incident waves with both Fabry-Perot oscillations inside the junctions and induced surface acoustic waves between the homogeneous part of the plate and the row of holes. With two rows of holes, low frequency peaks and dips appear in the transmission spectrum. The choice of the distance between the two rows of holes allows the realization of a broadband low frequency acoustic shielding with attenuation over 99% for symmetric waves in a wide low frequency range and over 90% for antisymmetric ones. The origin of the transmission gap is discussed in terms of localized modes of the "H" element made by the junctions, connecting the two homogeneous parts of the plate.
Stability analysis of two phase stratified flow in a rectangular channel
NASA Astrophysics Data System (ADS)
Bhagavatula, Dinesh; S, Pushpavanam
2015-11-01
Two phase stratified flows arise in extraction operations in microfluidic systems. It is well established that stratified flows in between two infinite plates is always unstable. However such flows are experimentally observed in micro channels. To understand this paradox we perform a linear stability analysis of stratified two phase Poiseuille flow in a rectangular duct. A two-dimensional fully developed flow through the rectangular channel is considered. The linearized equations along with the boundary conditions in primitive variable formulation are numerically solved using Chebyshev collocation method. All the primitive variables, which are the velocity and pressure fields, are retained in the linearised governing equations. Since boundary conditions for disturbance pressure do not exist, the corresponding compatibility conditions derived from the Navier-Stokes equations are collocated both at the walls and the interface. The resulting eigen-value problem is solved using a shift and invert Arnoldi algorithm. The role of different parameters such as Aspect ratio, density ratio, viscosity ratio on the stability characteristics is analyzed. The stability results are validated in the limit of large Aspect Ratios. The flow fields are sought as a combination of Chebyshev polynomials in both y and z directions. Ministry of Human Resource and Development (MHDR).
Optical design through optimization using freeform orthogonal polynomials for rectangular apertures
NASA Astrophysics Data System (ADS)
Nikolic, Milena; Benítez, P.; Miñano, Juan C.; Grabovickic, D.; Liu, Jiayao; Narasimhan, B.; Buljan, M.
2015-09-01
With the increasing interest in using freeform surfaces in optical systems due to the novel application opportunities and manufacturing techniques, new challenges are constantly emerging. Optical systems have traditionally been using circular apertures, but new types of freeform systems call for different aperture shapes. First non-circular aperture shape that one can be interested in due to tessellation or various folds systems is the rectangular one. This paper covers the comparative analysis of a simple local optimization of one design example using different orthogonalized representations of our freeform surface for the rectangular aperture. A very simple single surface off-axis mirror is chosen as a starting system. The surface is fitted to the desired polynomial representation, and the whole system is then optimized with the only constraint being the effective focal length. The process is repeated for different surface representations, amongst which there are some defined inside a circle, like Forbes freeform polynomials, and others that can be defined inside a rectangle like a new calculated Legendre type polynomials orthogonal in the gradient. It can be observed that with this new calculated polynomial type there is a faster convergence to a deeper minimum compared to "defined inside a circle" polynomials. The average MTF values across 17 field points also show clear benefits in using the polynomials that adapted more accurately to the aperture used in the system.
Underwood, H R; Peterson, A F; Magin, R L
1992-02-01
A rectangular microstrip antenna radiator is investigated for its near-zone radiation characteristics in water. Calculations of a cavity model theory are compared with the electric-field measurements of a miniature nonperturbing diode-dipole E-field probe whose 3 mm tip was positioned by an automatic three-axis scanning system. These comparisons have implications for the use of microstrip antennas in a multielement microwave hyperthermia applicator. Half-wavelength rectangular microstrip patches were designed to radiate in water at 915 MHz. Both low (epsilon r = 10) and high (epsilon r = 85) dielectric constant substrates were tested. Normal and tangential components of the near-zone radiated electric field were discriminated by appropriate orientation of the E-field probe. Low normal to transverse electric-field ratios at 3.0 cm depth indicate that the radiators may be useful for hyperthermia heating with an intervening water bolus. Electric-field pattern addition from a three-element linear array of these elements in water indicates that phase and amplitude adjustment can achieve some limited control over the distribution of radiated power. PMID:1612617
Underwood, H.R. ); Peterson, A.F. ); Magin, R.L. )
1992-02-01
A rectangular microstrip antenna radiator is investigated for its near-zone radiation characteristics in water. Calculations of a cavity model theory are compared with the electric-field measurements of a miniature nonperturbing diode dipole E-field probe whose 3 mm tip was positioned by an automatic three-axis scanning system. These comparisons have implications for the use of microstrip antennas in a multielement microwave hyperthermia applicator. Half-wavelength rectangular microstrip patches were designed to radiate in water at 915 MHz. Both low ([epsilon][sub r] = 10) and high ([epsilon][sub r] = 85) dielectric constant substrates were tested. Normal and tangential components of the near-zone radiated electric field were discriminated by appropriate orientation of the E-field probe. Low normal to transverse electric-field ratios ar 3.0 cm depth indicate that the radiators may be useful for hyperthermia heating with an intervening water bolus. Electric-field pattern addition from a three-element linear array of these elements in water indicates that phase and amplitude adjustment can achieve some limited control over the distribution of radiated power.
NASA Astrophysics Data System (ADS)
Yang, Ziqiang; Yang, Tao; Liu, Yu; Peng, Hao
2016-06-01
In this paper, a compact full Ka-band differential microstrip line (DML) to rectangular waveguide transition is proposed. The dipole antenna with semi-elliptic arms is introduced to transform the differential mode of DML to the TE10 mode of the rectangular waveguide directly. The two arms of the dipole antenna are connected together by a shorting strip to reduce the size of the dipole. Compared with the DML-to-waveguide transition using the fin-line topology, the size of the proposed transition has been reduced by 86 %. To verify this transition, a back-to-back structure is fabricated and tested. It provides a return loss of better than 15.2 dB and an insertion loss of 0.73 to 1.07 dB within a wide frequency range from 26.5 to 40 GHz. The measurement results show good agreement with the simulation results. Furthermore, a tolerance analysis is also performed via the simulation to prove that this transition is robust in the fabrication and mechanical assembly.
NASA Astrophysics Data System (ADS)
Awodola, T. O.; Omolofe, B.
2014-09-01
The dynamic response to moving concentrated masses of elastically supported rectangular plates resting on Winkler elastic foundation is investigated in this work. This problem, involving non-classical boundary conditions, is solved and illustrated with two common examples often encountered in engineering practice. Analysis of the closed form solutions shows that, for the same natural frequency (i) the response amplitude for the moving mass problem is greater than that one of the moving force problem for fixed Rotatory inertia correction factor R0 and foundation modulus F0, (ii) The critical speed for the moving mass problem is smaller than that for the moving force problem and so resonance is reached earlier in the former. The numerical results in plotted curves show that, for the elastically supported plate, as the value of R0 increases, the response amplitudes of the plate decrease and that, for fixed value of R0, the displacements of the plate decrease as F0 increases. The results also show that for fixed R0 and F0, the transverse deflections of the plates under the actions of moving masses are higher than those when only the force effects of the moving load are considered. Hence, the moving force solution is not a save approximation to the moving mass problem. Also, as the mass ratio Γ approaches zero, the response amplitude of the moving mass problem approaches that one of the moving force problem of the elastically supported rectangular plate resting on constant Winkler elastic foundation.
Rapid calculations of time-harmonic nearfield pressures produced by rectangular pistons.
McGough, Robert J
2004-05-01
A rapid method for calculating the nearfield pressure distribution generated by a rectangular piston is derived for time-harmonic excitations. This rapid approach improves the numerical performance relative to the impulse response with an equivalent integral expression that removes the numerical singularities caused by inverse trigonometric functions. The resulting errors are demonstrated in pressure field calculations using the time-harmonic impulse response solution for a rectangular source 5 wavelengths wide by 7.5 wavelengths high. Simulations using this source geometry show that the rapid method eliminates the singularities introduced by the impulse response. The results of pressure field computations are then evaluated in terms of relative errors and computational speeds. The results show that, when the same number of Gauss abscissas are applied to both approaches for time-harmonic pressure field calculations, the rapid method is consistently faster than the impulse response, and the rapid method consistently produces smaller maximum errors than the impulse response. For specified maximum error values of 10% and 1%, the rapid method is 2.6 times faster than the impulse response for pressure field calculations performed on a 61 by 101 point grid. The rapid approach achieves even greater reductions in the computation time for smaller errors and larger grids. PMID:15139602
An experimental investigation of flow boiling in an asymmetrically heated rectangular microchannel
Huh, Cheol; Kim, Moo Hwan
2006-08-15
By using unique experimental techniques and carefully constructed experimental apparatus, the characteristics of flow boiling of water in microscale were investigated using a single horizontal rectangular microchannel. A polydimethylsiloxane rectangular microchannel (D{sub h}=103.5 and 133{mu}m) was fabricated by using the replica molding technique, a kind of soft lithography. A piecewise serpentine platinum microheater array on a Pyrex substrate was fabricated with the surface micromachining MEMS technique. Real time flow visualization of the phase change phenomena inside the microchannel was performed using a high speed CCD camera with microscope. The experimental local boiling heat transfer coefficients were studied, and single bubble inception, growth, and departure, as well as elongated bubble behavior were analyzed to elucidate the microscale heat transfer mechanisms. Tests were performed for mass fluxes of 77.5, 154.9, and 309.8kg/m{sup 2}s and heat fluxes of 180-500kW/m{sup 2}. The effects of mass flux, heat flux, and vapor qualities on flow boiling heat transfer in a microchannel were studied. (author)
Analysis of components effecting free convection intensity in steel rectangular sections
NASA Astrophysics Data System (ADS)
Wyczółkowski, Rafał
2015-09-01
Free convection is one of the heat transfer modes which occurs within the heat-treated bundles of steel rectangular section. A comprehensive study of this phenomenon is necessary for optimizing the heating process of this type of charge. The free convection intensity is represented by the Rayleigh number Ra. The value of this criterion depends on the following parameters: the mean section temperature, temperature difference within the section, kinematic coefficient of viscosity, volume expansion coefficient and the Prandtl number. The paper presents the analysis of the impact of these factors on free convection in steel rectangular sections. The starting point for this analysis were the results of experimental examinations. It was found that the highest intensity of this process occurs for the temperature of 100 °C. This is mainly caused by changes in the temperature difference observed in the area of sections and changes in kinematic coefficient of viscosity of air. The increase in the value of the Rayleigh number criterion at the initial stage is attributable to changes in the parameter of temperature difference within the section. After exceeding 100 °C, the main effect on convection is from changes in air viscosity. Thus, with further increase in temperature, the Rayleigh number starts to decline rapidly despite further rise in the difference in temperature.
Karhunen-Loève basis of Kolmogorov phase screens covering a rectangular stripe
NASA Astrophysics Data System (ADS)
Mathar, Richard J.
2010-01-01
Karhunen-Loève functions are statistically independent base functions to be multiplied with randomized coefficients to generate instances of the underlying statistics with specific covariances. In the context of numerical simulation of atmospheric turbulence, they are tools to generate phase distributions in the input pupil of telescope optics. Within the Taylor frozen screen approximation, the favorable geometry of phase screens is a stripe as wide as the telescope diameter, but much longer. A phase screen movie is generated by dragging the stripe across the telescope pupil. The aim is to avoid the wasteful alternative of cutting through a virtual circular phase screen with a diameter equal to the stripe's length. We calculate Karhunen-Loève functions over rectangular stripes by solving the well-known integral equation for isotropic variance of the phase distribution. They are expanded in products of Legendre functions along the two Cartesian coordinates, represented by spherical Bessel functions in Fourier space. The rectangular shape of the integral's domain breaks the symmetry of the structure function. Yet, the matrix elements of the eigenvalue equation can be calculated by separating the primitive Cartesian basis via a Neumann series of radial and azimuthal terms.
Rapid calculations of time-harmonic nearfield pressures produced by rectangular pistons
McGough, Robert J.
2007-01-01
A rapid method for calculating the nearfield pressure distribution generated by a rectangular piston is derived for time-harmonic excitations. This rapid approach improves the numerical performance relative to the impulse response with an equivalent integral expression that removes the numerical singularities caused by inverse trigonometric functions. The resulting errors are demonstrated in pressure field calculations using the time-harmonic impulse response solution for a rectangular source 5 wavelengths wide by 7.5 wavelengths high. Simulations using this source geometry show that the rapid method eliminates the singularities introduced by the impulse response. The results of pressure field computations are then evaluated in terms of relative errors and computational speeds. The results show that, when the same number of Gauss abscissas are applied to both approaches for time-harmonic pressure field calculations, the rapid method is consistently faster than the impulse response, and the rapid method consistently produces smaller maximum errors than the impulse response. For specified maximum error values of 10% and 1%, the rapid method is 2.6 times faster than the impulse response for pressure field calculations performed on a 61 by 101 point grid. The rapid approach achieves even greater reductions in the computation time for smaller errors and larger grids. PMID:15139602
An analytical solution for Dean flow in curved ducts with rectangular cross section
NASA Astrophysics Data System (ADS)
Norouzi, M.; Biglari, N.
2013-05-01
In this paper, a full analytical solution for incompressible flow inside the curved ducts with rectangular cross-section is presented for the first time. The perturbation method is applied to solve the governing equations and curvature ratio is considered as the perturbation parameter. The previous perturbation solutions are usually restricted to the flow in curved circular or annular pipes related to the overly complex form of solutions or singularity situation for flow in curved ducts with non-circular shapes of cross section. This issue specifies the importance of analytical studies in the field of Dean flow inside the non-circular ducts. In this study, the main flow velocity, stream function of lateral velocities (secondary flows), and flow resistance ratio in rectangular curved ducts are obtained analytically. The effect of duct curvature and aspect ratio on flow field is investigated as well. Moreover, it is important to mention that the current analytical solution is able to simulate the Taylor-Görtler and Dean vortices (vortices in stable and unstable situations) in curved channels.
Refractive index sensing characteristics of dual resonances in rectangular fractal nano-apertures
NASA Astrophysics Data System (ADS)
Aslan, Ekin; Turkmen, Mustafa
2015-08-01
Aperture based sensing platforms can be useful for both gas and bio-sensing applications. In this study, we investigate the refractive index sensing characteristics of dual resonances in rectangular fractal nanoapertures. By taking the advantages coming from its aperture based nature and dual band resonant behavior, one can use this platform to detect two different chemical/bio-molecules simultaneously. For the numerical analysis, we study the rectangular fractal nanoantenna array through the finite difference time domain (FDTD) method. We also introduce a fine tuning mechanism for adjusting the resonance frequencies which is important for the sensing applications. Then, we demonstrate the results of refractive index sensitivity tests in order to show the behavior of the structure against the refractive index changes. In these tests, we embed our sensing platform into different cladding media and obtain the refractive index sensing characteristics of dual resonances. Due to the dual-resonant behavior with easily accessible ultra-high-field localization characteristics, the proposed sensing platform can be a good candidate for ultra-sensitive chemical- and bio-sensing applications.
Quasi-optimal locations of piezo-elements on a rectangular plate
NASA Astrophysics Data System (ADS)
Koszewnik, Andrzej; Gosiewski, Zdzisław
2016-07-01
The optimal location of piezo-actuators and piezo-sensors for the vibration control of a rectangular plate with SFSF (Simply Supported - Free - Simply Supported - Free) boundary conditions is presented in the paper. Based on bending moments, Mx(x,y) and My(x,y), the modal control forces generated by the piezo-stripes are calculated for the first five mode shapes. Calculations are carried out for different locations of two piezo-strips directed along the X and Y axes. The obtained results are used to define performance indexes of modal control forces for the two considered directions of vibration. In a similar way the modal unit elongations of the piezo-sensors are calculated for two different orientations of the piezos on the plate. Based on these results the objective cost functions J_{ɛ - odd} and J_{ɛ - even} are defined separately for odd and even modes. The quasi-optimal locations of the piezo-actuators and piezo-sensors are determined by maximizing the proposed cost functions. After analytical and numerical investigations the process of the full model identification is carried out at the laboratory stand. A chirp signal is applied in the identification process. The rectangular plate is excited with the chirp force while output signals are measured by the piezo-sensors oriented in the perpendicular directions X and Y. In such a way two mathematical models are obtained to control the vibration of the plate separately for odd and even natural modes.-1
Yarmand, Hooman; Gharehkhani, Samira; Kazi, Salim Newaz; Sadeghinezhad, Emad; Safaei, Mohammad Reza
2014-01-01
Thermal characteristics of turbulent nanofluid flow in a rectangular pipe have been investigated numerically. The continuity, momentum, and energy equations were solved by means of a finite volume method (FVM). The symmetrical rectangular channel is heated at the top and bottom at a constant heat flux while the sides walls are insulated. Four different types of nanoparticles Al2O3, ZnO, CuO, and SiO2 at different volume fractions of nanofluids in the range of 1% to 5% are considered in the present investigation. In this paper, effect of different Reynolds numbers in the range of 5000 < Re < 25000 on heat transfer characteristics of nanofluids flowing through the channel is investigated. The numerical results indicate that SiO2-water has the highest Nusselt number compared to other nanofluids while it has the lowest heat transfer coefficient due to low thermal conductivity. The Nusselt number increases with the increase of the Reynolds number and the volume fraction of nanoparticles. The results of simulation show a good agreement with the existing experimental correlations. PMID:25254236
Xiao, Junyan; Li, Zhe; Ye, Xiaozhou; Ma, Yurong; Qi, Limin
2014-01-21
Vertically aligned, supercrystalline microplates with a well-defined rectangular shape were fabricated in a large area through self-assembly of gold nanorods by a novel bulk solution evaporation method. This evaporative self-assembly strategy involving continuous movement of the contact line can prevent the coffee-ring effect, thus allowing uniform deposition of discrete GNR superstructures over a large area and favoring the formation of GNR supercrystals with geometrically symmetric shapes. A mechanism based on the continuing nucleation and growth of smectic GNR superstructures accompanying the movement of the contact line was put forward for the formation of the unique GNR supercrystal arrays. Based on this mechanism, a micropatterned substrate was designed to control the nucleation location and growth direction, leading to the spontaneous self-assembly of nearly parallel arrays of vertically aligned, supercrystalline microplates of GNRs. The obtained rectangular-plate-shaped GNR supercrystals exhibited interesting anisotropic optical reflection properties, which were revealed by polarized light microscopy. PMID:24292548
Kazi, Salim Newaz; Sadeghinezhad, Emad
2014-01-01
Thermal characteristics of turbulent nanofluid flow in a rectangular pipe have been investigated numerically. The continuity, momentum, and energy equations were solved by means of a finite volume method (FVM). The symmetrical rectangular channel is heated at the top and bottom at a constant heat flux while the sides walls are insulated. Four different types of nanoparticles Al2O3, ZnO, CuO, and SiO2 at different volume fractions of nanofluids in the range of 1% to 5% are considered in the present investigation. In this paper, effect of different Reynolds numbers in the range of 5000 < Re < 25000 on heat transfer characteristics of nanofluids flowing through the channel is investigated. The numerical results indicate that SiO2-water has the highest Nusselt number compared to other nanofluids while it has the lowest heat transfer coefficient due to low thermal conductivity. The Nusselt number increases with the increase of the Reynolds number and the volume fraction of nanoparticles. The results of simulation show a good agreement with the existing experimental correlations. PMID:25254236
Numerical and experimental study of shock waves emanating from an open-ended rectangular tube
NASA Astrophysics Data System (ADS)
Koroteeva, E. Yu.; Znamenskaya, I. A.; Glazyrin, F. N.; Sysoev, N. N.
2016-05-01
We examine the dynamics of a high-speed shock-induced flow near the open end of a shock tube using the particle image velocimetry (PIV) and the background oriented schlieren (BOS) methods along with two- and three-dimensional numerical simulations. In experiments, planar shock waves (M=1.3-1.6) are discharged from a rectangular (24 mm × 48 mm) low-pressure section of a shock tube open to the atmosphere. Due to the rectangular exit geometry, the resulting flow is highly three-dimensional and, thus, more complicated, compared to well-studied circular/axisymmetric geometries. The study focuses on the spatio-temporal flow structure up to 1 ms after the shock wave diffraction. PIV and BOS visualization techniques share the same post-processing principle, and the iterative multi-step cross-correlation algorithm applied in the PIV software is adapted here for the calculation of background pattern displacement on the BOS images. Particular attention is given to the resolution of flow regions where sharp gradients are present, such as a diffracted shock front or embedded shocks. Computational fluid dynamic simulations of the problem are also conducted to validate the experimental results and methods and to gain more insight into the three-dimensional flow dynamics. PIV and BOS images are found to be consistent with the corresponding numerical flow visualizations.
NASA Astrophysics Data System (ADS)
Xiong, Qihua; Eklund, P. C.
2005-03-01
Raman scattering from surface optic (SO) phonons has been observed and identified in cylindrical GaP and rectangular cross-section ZnS nanowires. We propose that the symmetry breaking mechanism which activates the SO phonon is a periodic modulation of the cross-sectional area along the nanowires. In the case of cylindrical GaP nanowires, Raman scattering from SO phonons in air at room temperature is observed at 394 cm-1, in between the first order longitudinal optic (LO) (401 cm-1) and transverse optic (TO) (367 cm-1), and downshift to 392 cm-1 in dichloromethane (?m=2.0) and 390 cm-1 in aniline (?m=2.56). Raman scattering from the ZnS nanowires in air at room temperature reveals a strong first-order LO mode at 346 cm-1 and two TO modes at 269 and 282 cm-1. The SO Raman band in ZnS is observed at 335 cm-1 in air, and downshifts to 328 cm-1 in dichloromethane and to 326 cm-1 in aniline. The position of the SO band in GaP and ZnS nanowires is consistent with a dielectric continuum model. Theoretical SO phonon dispersion for both cylindrical and rectangular cross-section nanowires is presented and compared to experiment. This work was supported by the NSF NIRT program (DMR- 0304178).
Seon, Jong-Keun; Song, Eun-Kyoo; Park, Sang-Jin; Lee, Dam-Seon
2011-06-01
The authors evaluated 112 knees treated by total knee arthroplasty (TKA) using a navigation-assisted modified gap balancing technique. Initial mediolateral gap differences in extension and in 90° of flexion were measured after proximal tibia bone cutting. Final flexion and extension gaps were measured by checking distances under equal tension before prosthesis insertion. Amount of femoral bone cutting and external rotations of femoral components were found to depend on initial gaps. Patients with a final rectangular gap had greater knee flexion angles preoperatively and at 1 year after TKA. However, no differences were observed between the clinical and radiologic outcomes of knees with rectangular and nonrectangular gaps at 1 or 4 years after TKA. The study shows that the navigation-assisted modified gap balancing technique provides an effective means of achieving rectangular flexion and extension gaps during TKA. PMID:20580194
Miyazaki, H; Makiguchi, T; Takayama, Y; Yokoo, S
2014-09-01
The use of a rectangular flap is a well known technique for upper lip repair in cleft lip, but is less common for lower lip repair after tumour resection. We have found this type of flap to be favourable for lower lip reconstruction, especially for the lip to mental region. We describe herein an improvement to the technique in which two opposing rectangular flaps, with the length of one side equal to the vertical distance from the mentolabial groove to the vermilion border, were raised on the lateral sides of a U-shaped defect. Reconstruction was performed by interdigitation of the two flaps and a bilateral vermilion advancement flap. This new approach allows a distinct mentolabial groove and mental protuberance to be created by utilizing two opposing rectangular flaps and redundant tissue, without sacrificing sensation and muscle function. Our results suggest that the technique provides excellent functional and cosmetic outcomes in restoration of the lower lip in properly selected patients. PMID:24997680
NASA Astrophysics Data System (ADS)
Hu, Yang; Yang, Qing; Chen, Feng; Bian, Hao; Deng, Zefang; Du, Guangqing; Si, Jinhai; Yun, Feng; Hou, Xun
2014-02-01
This paper presents a cost-efficient and flexible approach to the development of controllable-shape concave and convex microlens arrays by using femtosecond laser wet etch and replication techniques. Periodic concave rectangular-shaped microlens arrays with different length-width ratios were achieved by firstly introducing periodic microcraters on silica glass using an 800 nm femtosecond laser, and subsequently enlarging the craters into microlens with smooth curved surfaces in hydrofluoric (HF) acid solution. The concave microlens can serve as molds of replication to obtain convex microlenses on polymers. Over 10,000 rectangular-shaped concave and convex microlens with controllable aspect ratio, high fill factor and spherical morphology can be fabricated in 5 h. A simulation result and a projection experiment result verify the optical performance of these rectangular-shaped spherical microlens arrays (MLAs).
NASA Astrophysics Data System (ADS)
Yoneda, K.; Shirai, Y.; Shiotsu, M.; Oura, Y.; Horie, Y.; Matsuzawa, T.; Shigeta, H.; Tatsumoto, H.; Hata, K.; Naruo, Y.; Kobayashi, H.; Inatani, Y.
In this report, we show results on the forced flow boiling heat transfer experiments for manganin plate pasted on one side of a rectangular duct. Nucleate boiling heat transfer and its Departure from Nucleate Boiling (DNB) heat flux were measured for various pressures, subcooling and flow velocities. The DNB heat fluxes are higher for higher subcooling and higher flow velocity. The DNB heat fluxes were compared with the experimental data for round tube of nearly equal equivalent diameter. The DNB heat fluxes for the rectangular duct are lower than those for the round tube.
NASA Astrophysics Data System (ADS)
Zhang, Shangyu; Cheng, Renxiang; Tao, Chao; Liu, Xiaojun
2016-04-01
The enlargement of the field of view (FOV) of a photoacoustic (PA) tomography (PAT) system and the improvement of its lateral resolution are often two conflicting goals. A rectangular focused transducer is proposed to solve this problem. An asymmetric geometry of the transducer results in its asymmetric characteristics of the ultrasound (US) field. Both simulation and experiments confirm that the rectangular focused transducer can improve the FOV and lateral resolution of PAT systems simultaneously. The US transducer proposed in this study has the potential to improve the performance of a PAT system for practical biomedical applications.
NASA Technical Reports Server (NTRS)
Vaidya, P. G.; Wang, K. S.
1977-01-01
Nonlinear acoustic interactions at the second order (so-called weak interactions) of the perturbation scheme have been recognized for a long time. This paper examines the possibility of stronger interactions at the first order which are found in rigid rectangular ducts and to a lesser degree in slightly soft rectangular ducts. The strong interactions occur if any two modes have identical phase speeds, the case of multimode and multifrequency input for example. An important consequence of the strong interaction is the self-generation of subharmonics. Even a small amount of subharmonic can, given the right phase conditions, grow through a strong interaction with a higher harmonic.
NASA Technical Reports Server (NTRS)
Vogel, J. M.
1973-01-01
The calculation of the outer inviscid flow about a rectangular wing moving at supersonic speeds is reported. The inviscid equations of motion governing the flow generated by the wing form a set of hyperbolic differential equations. The flow field about the rectangular wing is separated into three regions consisting of the forebody, the afterbody, and the wing wake. Solutions for the forebody are obtained using conical flow techniques while the afterbody and the wing wake regions are treated as initial value problems. The numerical solutions are compared in the two dimensional regions with known exact solutions.
Flow and turbulence structure around an in-stream rectangular cylinder with scour hole
NASA Astrophysics Data System (ADS)
Kirkil, Gokhan; Constantinescu, George
2010-11-01
Most of the erosion around obstacles present in alluvial streams takes place after the formation of a scour hole of sufficiently large dimensions to stabilize the large-scale oscillations of the horseshoe vortex (HV) system. The present paper uses eddy resolving techniques to reveal the unsteady dynamics of the coherent structures present in the flow field around an in-stream vertical cylinder (e.g., bridge pier) with a large scour hole at a channel Reynolds number defined with the channel depth and the bulk channel velocity of 2.4 × 105. The cylinder has a rectangular section and is placed perpendicular to the incoming flow. The geometry of the scour hole is obtained from an experiment conducted as part of the present work. The mechanisms driving the bed erosion during the advanced stages of the scour process around the vertical plate are discussed. Simulation results demonstrate the critical role played by these large-scale turbulent eddies and their interactions in driving the local scour. The paper analyzes the changes in the flow and turbulence structure with respect to the initial stages of the scour process (flat bed conditions) for a cylinder of identical shape and orientation. Results show the wake loses its undular shape due to suppression of the antisymmetrical shedding of the roller vortices. Also, the nature of the interactions between the necklace vortices of the HV system and the eddies present inside the detached shear layers (DSLs) changes as the scour process evolves. This means that information on the vortical structure of the flow at the initiation of the scour process, or during its initial stages, are insufficient to understand the local scour mechanisms. The paper also examines the effect of the shape of the obstruction on the dynamics of the vortical eddies and how it affects the bed erosion processes during the advanced stages of the local scour. In particular, the paper provides an explanation for the observed increase in the maximum
Linear and non-linear deflection analysis of thick rectangular plates. 2: Numerical applications
NASA Astrophysics Data System (ADS)
Bencharif, N.; Ng, S. F.
1994-03-01
Variational methods are widely used for the solution of complex differential equations in mechanics for which exact solutions are not possible. The finite difference method, although well known as an efficient numerical method, was applied in the past only for the analysis of linear and non-linear thin plates. In this paper the suitability of the method for the analysis of non-linear deflection of thick plates is studied for the first time. While there are major differences between small deflection and large deflection plate theories, the former can be treated as a particular case of the latter, when the centre deflection of the plate is less than or equal to 0.2-0.25 of the thickness of the plate. The finite difference method as applied here is a modified finite difference approach to the ordinary finite difference method generally used for the solution of thin plate problems. In this analysis thin plates are treated as a particular case of the corresponding thick plate when the boundary conditions of the plates are taken into account. The method is first applied to investigate the deflection behaviour of clamped and simply supported square isotropic thick plates. After the validity of the method is established, it is then extended to the solution of rectangular thick plates of various aspect ratios and thicknesses. Generally, beginning with the use of a limited number of mesh sizes for a given plate aspect ratio and boundary conditions, a general solution of the problem including the investigation of accuracy and convergence was extended to rectangular thick plates by providing more detailed functions satisfying the rectangular mesh sizes generated automatically by the program. Whenever possible results obtained by the present method are compared with existing solutions in the technical literature obtained by much more laborious methods and close agreements are found. The significant number of results presented here are not currently available in the technical
Azimipour, Mehdi; Atry, Farid; Pashaie, Ramin
2016-04-10
Digital optical phase conjugation (DOPC) has proven to be a promising technique in deep tissue fluorescence imaging. Nonetheless, DOPC optical setups require precise alignment of all optical components to accurately read the wavefront of scattered light in a turbid medium and playback the conjugated beam toward the sample. Minor misalignments and possible imperfections in the arrangement or the structure of the optical components significantly reduce the performance of the method. In this paper, a calibration procedure based on orthogonal rectangular polynomials is introduced to compensate major imperfections including the optical aberration in the wavefront of the reference beam and the substrate curvature of the spatial light modulator without adding extra optical components to the original setup. The proposed algorithm also provides a systematic calibration procedure for mechanical fine tuning of DOPC systems. It is shown experimentally that the proposed calibration process improves the peak-to-background ratio when focusing light after passing through a highly scattering medium. PMID:27139849
Thermal Buckling Analysis of Rectangular Panels Subjected to Humped Temperature Profile Heating
NASA Technical Reports Server (NTRS)
Ko, William I.
2004-01-01
This research investigates thermal buckling characteristics of rectangular panels subjected to different types of humped temperature profile heating. Minimum potential energy and finite-element methods are used to calculate the panel buckling temperatures. The two methods give fairly close thermal buckling solutions. 'Buckling temperature magnification factor of the first kind, eta' is established for the fixed panel edges to scale up the buckling solution of uniform temperature loading case to give the buckling solution of the humped temperature profile loading cases. Also, 'buckling temperature magnification factor of the second kind, xi' is established for the free panel edges to scale up the buckling solution of humped temperature profile loading cases with unheated boundary heat sinks to give the buckling solutions when the boundary heat sinks are heated up.
NASA Astrophysics Data System (ADS)
Koita, T.; Zhu, Y.; Sun, M.
2016-05-01
This paper reports an experimental investigation on the effects of explosion depth and tube width on the water jet induced by an underwater electrical discharge in a narrow rectangular tube. The water jet formation and bubble structure were evaluated from the images recorded by a high-speed video camera. Two typical patterns of jet formation and four general patterns of bubble implosion were observed, depending on the explosion depth and tube width. The velocity of the water jet was calculated from the recorded images. The jet velocity was observed to depend on not only the explosion depth and energy, but also on the tube width. We proposed an empirical formula defining the water jet velocity in the tube as a function of the tube width and explosion depth and energy.
NASA Astrophysics Data System (ADS)
Chen, Dongliang; Sun, Jinhua; Chen, Sining; Liu, Yi; Chu, Guanquan
2007-01-01
In order to explore the flame propagation characteristics and tulip flame formation mechanism of premixed methane/air mixture in horizontal rectangular ducts, the techniques of Schlieren and high-speed video camera are used to study the flame behaviors of the premixed gases in a closed duct and opened one respectively, and the propagation characteristics in both cases and the formation mechanism of the tulip flame are analyzed. The results show that, the propagation flame in a closed duct is prior to form a tulip flame structure than that in an opened duct, and the tulip flame structure formation in a closed duct is related to the flame propagation velocity decrease. The sharp decrease of the flame propagation velocity is one of the reasons to the tulip flame formation, and the decrease of the flame propagation velocity is due to the decrease of the burned product flow velocity mainly.
Soret-driven convection of ternary mixtures in a rectangular cavity
NASA Astrophysics Data System (ADS)
Lyubimova, Tatyana; Zubova, Nadezhda
2012-07-01
Soret-driven convection of ternary mixtures in a rectangular cavity is studied for different levels of static and vibrational accelerations and different orientations of temperature gradient. The problem is solved numerically by finite difference method. The transformation eliminating cross-diffusion effects for multicomponent mixtures is implemented which allows to reduce the number of governing parameters. The calculations are performed for hydrocarbon mixtures tetrahydronaphtalene-isobutylbenzene-dodecane with different mass fractions of components. These mixtures have positive separation ratios, therefore due to Soret effect dodecane and isobutylbenzene move to the warmer domains and tetrahydronaphtalene to the colder domain. Numerical data on temporal evolution of the velocity, temperature and concentration fields and characteristics of steady states are obtained for different parameter values. The work was done under financial support of Government of Perm Region, Russia (Contract C-26/212).
Signal modeling in low coherence interference microscopy on example of rectangular grating.
Xie, Weichang; Lehmann, Peter; Niehues, Jan; Tereschenko, Stanislav
2016-06-27
Besides the illumination wavelength also the numerical aperture (NA) of a microscope objective affects the fringe spacing in interference microscopy. Therefore, at high NA values an effective wavelength should be obtained by calibration. At step height structures both, the effective wavelength and the batwing effect strongly depend on the height-to-wavelength-ratio (HWR). Therefore, changes of the effective wavelength considering temporal and spatial coherence enable us to estimate the batwing effect in measurement results. For high NA systems and broadband illumination two different theoretical approaches for signal modeling are introduced to study the influence of the center wavelength, the temporal, and the spatial coherence of the illuminating light on measurement results of a rectangular grating. In both models diffraction is considered. While the first simulation model (Kirchhoff) is mostly analytical the second one (Richards-Wolf) is primarily numerical. Simulation results of both models show a good agreement with experimental measurement results. PMID:27410584
Acoustic response of a rectangular waveguide with a strong transverse temperature gradient
NASA Technical Reports Server (NTRS)
Zorumski, William E.
1989-01-01
An acoustic wave equation was developed for a perfect gas with spatially-variable temperature. The strong-gradient wave equation was used to analyze the response of a rectangular wave guide containing a thermally-stratified gas. It was assumed that the temperature gradient is constant, representing one-dimensional heat transfer with a constant coefficient of conductivity. The analysis of the waveguide shows that the resonant frequencies of the waveguide are shifted away from the values that would be expected from the average temperature of the waveguide. For small gradients, the frequency shift is proportional to the square of the gradient. The factor of proportionality is a quadratic function of the natural frequency of the waveguide with uniform temperature. An experiment is designed to verify the essential features of the strong-gradient theory.
Shock wave bifurcation in convergent-divergent channels of rectangular cross section
NASA Astrophysics Data System (ADS)
Kuzmin, A.
2016-02-01
This work addresses two- and three-dimensional turbulent flow in simple channels, modeling the air intakes of rectangular cross section. Flow regimes with a supersonic free stream and supersonic velocities at the throat or immediately downstream of the throat are considered. Bifurcations of the shock wave arising ahead of the cowl are studied numerically. Solutions of the Reynolds-averaged Navier-Stokes equations are obtained with a finite-volume solver of second-order accuracy on fine computational meshes. The solutions reveal jumps of the shock leg position with variations of the free-stream Mach number. The dependence of the shock position on the cowl slope and streamwise location of the throat is examined.
NASA Astrophysics Data System (ADS)
Ha, Dong-Gwang; Park, Jung; Jun, So-Yeon; Song, Woon; Chong, Yonuk
2013-03-01
We present our design, fabrication and characterization of superconducting transmon qubits and resonators for circuit quantum electrodynamics (QED). We have made coplanar waveguide resonators and rectangular waveguide resonators. The characteristics of the resonators are well controlled by the design parameters, with the fundamental frequencies in the range of 1 to 8 GHz and the quality factors in the range of 102 to 106, respectively. We measured the resonator characteristics as a function of temperature. The excitation power dependence of the resonator characteristics was also investigated. For transmon qubits, we fabricated 100 nm-scale Al/Al2Ox/Al tunnel junctions with e-beam lithography and double angle evaporation. The junctions were characterized at low temperature down to 10 mK. Furthermore, quantum state measurement and manipulation in circuit QED structure will be discussed.
In-plane vibrations of a rectangular plate: Plane wave expansion modelling and experiment
NASA Astrophysics Data System (ADS)
Arreola-Lucas, A.; Franco-Villafañe, J. A.; Báez, G.; Méndez-Sánchez, R. A.
2015-04-01
Theoretical and experimental results for in-plane vibrations of a uniform rectangular plate with free boundary conditions are obtained. The experimental setup uses electromagnetic-acoustic transducers and a vector network analyzer. The theoretical calculations were obtained using the plane wave expansion method applied to the in-plane thin plate vibration theory. The agreement between theory and experiment is excellent for the lower 95 modes covering a very wide frequency range from DC to 20 kHz. Some measured normal-mode wave amplitudes were compared with the theoretical predictions; very good agreement was observed. The excellent agreement of the classical theory of in-plane vibrations confirms its reliability up to very high frequencies
Effect of varying internal geometry on the static performance of rectangular thrust-reverser ports
NASA Technical Reports Server (NTRS)
Re, Richard J.; Mason, Mary L.
1987-01-01
An investigation has been conducted to evaluate the effects of several geometric parameters on the internal performance of rectangular thrust-reverser ports for nonaxisymmetric nozzles. Internal geometry was varied with a test apparatus which simulated a forward-flight nozzle with a single, fully deployed reverser port. The test apparatus was designed to simulate thrust reversal (conceptually) either in the convergent section of the nozzle or in the constant-area duct just upstream of the nozzle. The main geometric parameters investigated were port angle, port corner radius, port location, and internal flow blocker angle. For all reverser port geometries, the port opening had an aspect ratio (throat width to throat height) of 6.1 and had a constant passage area from the geometric port throat to the exit. Reverser-port internal performance and thrust-vector angles computed from force-balance measurements are presented.
Husnik, Martin; Niegemann, Jens; Busch, Kurt; Wegener, Martin
2013-11-15
By using a recently introduced approach combining a focus-modulation technique with a common-path interferometer, we measure quantitatively the extinction, scattering, and absorption cross-section spectra of individual optical antennas. The experimental results on thin-wire antennas, slot antennas, bow-tie antennas, rectangular antennas, and square-shaped antennas resonating at around 1.4 μm wavelength are discussed. We find increased resonant scattering cross sections for the latter four antennas compared to the thin-wire antenna, both in absolute terms and relative to the absorption cross section. The square-shaped antenna's resonant extinction cross section approaches the limit of a coherent point dipole. However, the ratio of the resonant extinction cross section to the geometrical cross section of 38 is largest for the simple thin-wire antenna. PMID:24322083
Liquid-metal flow in a rectangular duct with a non-uniform magnetic field
Walker, J.S.
1986-04-01
This paper treats liquid-metal flow in rectangular ducts with thin conducting walls. A transverse magnetic field changes from a uniform strength upstream to a weaker uniform strength downstream. The Hartmann number and the interaction parameter are assumed to be large, while the magnetic Reynolds number is assumed to be small. If the magnetic field changes gradually over a long duct length, the velocity and pressure are nearly uniform in each cross section and the flow differs slightly from locally fully developed flow. If the magnetic field changes more abruptly over a shorter duct length, the velocity and pressure are much larger near the walls parallel to the magnetic field than in the central part of duct. Solutions for the pressure drops due to the magnetic field change are presented.
NASA Astrophysics Data System (ADS)
Hu, Dan; Chen, Bing
2015-11-01
The extraordinary transmission (ET) due to localized surface plasmon (LSP) and propagating surface plasmon (PSP) resonances of terahertz wave through a copper film perforated with circular and rectangular apertures is investigated theoretically and experimentally. Considering that the field distributions of LSP and PSP resonances are determined by the shape and periods of the apertures on the film, the relations between extraordinary and the geometrical parameters of the apertures are investigated. The intensities of the ETs induced by the PSP resonances mode [1, 1] are much stronger than the fundamental ones [1, 0] and [0, 1]. Our finds provide another effective method to tailor the extraordinary THz transmission in sub-wavelength metallic aperture structures.
Li, Rui; Wang, Pengcheng; Tian, Yu; Wang, Bo; Li, Gang
2015-01-01
A unified analytic solution approach to both static bending and free vibration problems of rectangular thin plates is demonstrated in this paper, with focus on the application to corner-supported plates. The solution procedure is based on a novel symplectic superposition method, which transforms the problems into the Hamiltonian system and yields accurate enough results via step-by-step rigorous derivation. The main advantage of the developed approach is its wide applicability since no trial solutions are needed in the analysis, which is completely different from the other methods. Numerical examples for both static bending and free vibration plates are presented to validate the developed analytic solutions and to offer new numerical results. The approach is expected to serve as a benchmark analytic approach due to its effectiveness and accuracy. PMID:26608602
Warren, Richard M.; Bashford, James A.; Lenz, Peter W.
2011-01-01
There is a need, both for speech theory and for many practical applications, to know the intelligibilities of individual passbands that span the speech spectrum when they are heard singly and in combination. While indirect procedures have been employed for estimating passband intelligibilities (e.g., the Speech Intelligibility Index), direct measurements have been blocked by the confounding contributions from transition band slopes that accompany filtering. A recent study has reported that slopes of several thousand dBA/octave produced by high-order finite impulse response filtering were required to produce the effectively rectangular bands necessary to eliminate appreciable contributions from transition bands [Warren et al., J. Acoust. Soc. Am. 115, 1292–1295 (2004)]. Using such essentially vertical slopes, the present study employed sentences, and reports the intelligibilities of their six 1-octave contiguous passbands having center frequencies from 0.25 to 8 kHz when heard alone, and for each of their 15 possible pairings. PMID:16334905
Computation of Three-Dimensional Compressible Flow From a Rectangular Nozzle with Delta Tabs
NASA Technical Reports Server (NTRS)
Reddy, D. R.; Steffen, C. J., Jr.; Zaman, K. B. M. Q.
1999-01-01
A three-dimensional viscous flow analysis is performed using a time-marching Reynolds-averaged Navier-Stokes code for a 3:1 rectangular nozzle with two delta tabs located at the nozz1e exit plane to enhance mixing. Two flow configurations, a subsonic jet case and a supersonic jet case using the same rate configuration, which were previously studied experimentally, are computed and compared with the experimental data. The experimental data include streamwise velocity and vorticity distributions for the subsonic case, and Mach number distributions for the supersonic case, at various axial locations downstream of the nozzle exit. The computational results show very good agreement with the experimental data. In addition, the effect of compressibility on vorticity dynamics is examined by comparing the vorticity contours of the subsonic jet case with those of the supersonic jet case which were not measured in the experiment.
Damping Solitary Wave in a Three-Dimensional Rectangular Geometry Plasma
NASA Astrophysics Data System (ADS)
Ren, Yanqiu; Li, Gun; Duan, Wenshan
2016-02-01
The solitary waves of a viscous plasma confined in a cuboid under the three types of boundary condition are theoretically investigated in the present paper. By introducing a three-dimensional rectangular geometry and employing the reductive perturbation theory, a quasi-KdV equation is derived in the viscous plasma and a damping solitary wave is obtained. It is found that the damping rate increases as the viscosity coefficient increases, or increases as the length and width of the rectangle decrease, for all kinds of boundary condition. Nevertheless, the magnitude of the damping rate is dominated by the types of boundary condition. We thus observe the existence of a damping solitary wave from the fact that its amplitude disappears rapidly for a → 0 and b → 0, or v‧ → + ∞. supported by National Natural Science Foundation of China (Nos. 91026005, 11275156, 11047010, 61162017)
Resonant Interaction of a Rectangular Jet with a Flat-Plate
NASA Technical Reports Server (NTRS)
Zaman, K. B. M. Q.; Fagan, A. F.; Clem, M. M.; Brown, C. A.
2014-01-01
A resonant interaction between a large aspect ratio rectangular jet and a flat-plate is addressed in this experimental study. The plate is placed parallel to but away from the direct path of the jet. At high subsonic conditions and for certain relative locations of the plate, the resonance accompanied by an audible tone is encountered. The trends of the tone frequency variation exhibit some similarities to, but also marked differences from, corresponding trends of the well-known edge-tone phenomenon. Under the resonant condition flow visualization indicates a periodic flapping motion of the jet column. Phase-averaged Mach number data obtained near the plate's trailing edge illustrate that the jet cross-section goes through large contortions within the period of the tone. Farther downstream a clear 'axis switching' takes place. These results suggest that the assumption of two-dimensionality should be viewed with caution in any analysis of the flow.
Snow, David E.; Kim, Dae Jung; Hope-Weeks, Louisa J.; Weeks, Brandon L.; Pitchimani, Rajasekar
2008-08-15
In order to address the issue of spring constant calibration in viscous fluids such as water, a new method is presented that allows for the experimental calibration of bimaterial cantilever spring constants. This method is based on modeling rectangular cantilever beam bending as a function of changing temperature. The temperature change is accomplished by heating water as it flows around the cantilever beams in an enclosed compartment. The optical static method of detection is used to measure the deflection of cantilever at the free end. Experimentally determined results are compared to Sader's method and to the Thermotune method most commonly used in cantilever calibrations. Results indicate that the new bimaterial thermal expansion method is accurate within 15%-20% of the actual cantilever spring constant, which is comparable to other nondestructive calibration techniques.
Finite amplitude vibrations of cantilevers of rectangular cross sections in viscous fluids
NASA Astrophysics Data System (ADS)
Phan, Catherine N.; Aureli, Matteo; Porfiri, Maurizio
2013-07-01
In this paper, we study finite amplitude vibrations of a cantilever beam of rectangular cross section immersed in a viscous fluid under harmonic base excitation. Fluid-structure interactions are modeled through a complex hydrodynamic function that describes added mass and damping effects in response to moderately large oscillation amplitudes. The hydrodynamic function is identified from the analysis of the two-dimensional flow physics generated by a rigid rectangle undergoing harmonic oscillations in a quiescent fluid. Computational fluid dynamics is used to investigate the effects of three salient non-dimensional parameters on the flow physics and inform the formulation of a tractable expression for the hydrodynamic function. Theoretical results are validated against experimental findings on underwater vibration of compliant beams of varying cross sections.
Study of compressible flow through a rectangular-to-semiannular transition duct
NASA Technical Reports Server (NTRS)
Foster, Jeffry; Okiishi, Theodore H.; Wendt, Bruce J.; Reichert, Bruce A.
1995-01-01
Detailed flow field measurements are presented for compressible flow through a diffusing rectangular-to-semiannular transition duct. Comparisons are made with published computational results for flow through the duct. Three-dimensional velocity vectors and total pressures were measured at the exit plane of the diffuser model. The inlet flow was also measured. These measurements are made using calibrated five-hole probes. Surface oil flow visualization and surface static pressure data were also taken. The study was conducted with an inlet Mach number of 0.786. The diffuser Reynolds based on the inlet centerline velocity and the exit diameter of the diffuser was 3,200,000. Comparison of the measured data with previously published computational results are made. Data demonstrating the ability of vortex generators to reduce flow separation and circumferential distortion is also presented.
NASA Astrophysics Data System (ADS)
Allen, A.; Steward, D. R.
2013-12-01
It is computationally advantageous when modeling large scale regional domains to be able to partition the domain into smaller, more mathematically tractable pieces. A convenient unit of discretization is a rectangle, for which separation of variable solutions exist. We apply the Analytic Element Method to develop a solution by covering the domain with such rectangular elements and then applying continuity conditions across adjacent rectangles to satisfy conservation of energy and mass. The resulting model is tested against a benchmark solution provided by the method of images to verify the accuracy of the solution. Results are presented for regional modeling of the High Plains Aquifer in southwestern Kansas, to illustrate the capacity of the model to perform regional modeling while still capturing the local detail of well-on-well interactions.
Influence of the synchrotron radiation on particle dynamics in a rectangular undulator
Chin, Yong Ho
1989-03-01
This paper is concerned with the synchrotron radiation from an undulating electron beam in a rectangular waveguide. It is shown analytically and numerically that the radiated energy spectrum may differ significantly from the free space result when the undulator length divided by the Lorentz factor of the electron beam is larger than the transverse size of the waveguide. The undulator radiation is identified with the awake field in beam instabilities. The concepts of wake function and impedance are introduced to formulate the present problem in the same manner as the beam instability problem. It is shown that the obtained impedances satisfy the Panofsky-Wenzel theorem and other properties inevitable for wake fields. 5 refs., 2 figs.
Starting vortex behavior in flow through a time-varying rectangular slit
NASA Astrophysics Data System (ADS)
Barry, Michael; Krane, Michael; Wei, Timothy
2006-11-01
The behavior of the starting vortex issuing from a time-varying rectangular slit with an imposed pressure gradient, representing the flow through the human glottis, is presented. The range of reduced frequency of vibration was 0.01-0.04 and the Reynolds number 8000. DPIV measurements of the velocity field on the plane of symmetry show that the starting vortex formation takes a longer fraction of the vibration period as the reduced frequency increases. The formation time and strength of the starting vortex are estimated from the velocity field measurements. In addition, the volume flow measurements allow the stroke ratio L/D to be estimated. The correlation L/D and pinch-off is also discussed.
Optimisation of the blank shape for micro deep drawing of rectangular parts
Hu Zhenyu; Vollertsen, Frank
2011-05-04
In this investigation the blank shape for micro deep drawing of rectangular parts was for the first time optimized using FEM method with consideration of the real process conditions in micro forming, i.e. the coefficient of friction and the flow curves of thin foils. The acquired optimized blank shape was then validated by applying it to experiments. For both numerical and experimental investigations a punch with a section of 2x1 mm{sup 2} was used. Aluminum Al99.5 with a sheet thickness of 20 {mu}m was used as blank material in this investigation. A flange free drawn part was successfully obtained from experiment using the blank shape and blank holder force optimized using FEM.
Snow, David E; Weeks, Brandon L; Kim, Dae Jung; Pitchimani, Rajasekar; Hope-Weeks, Louisa J
2008-08-01
In order to address the issue of spring constant calibration in viscous fluids such as water, a new method is presented that allows for the experimental calibration of bimaterial cantilever spring constants. This method is based on modeling rectangular cantilever beam bending as a function of changing temperature. The temperature change is accomplished by heating water as it flows around the cantilever beams in an enclosed compartment. The optical static method of detection is used to measure the deflection of cantilever at the free end. Experimentally determined results are compared to Sader's method and to the Thermotune method most commonly used in cantilever calibrations. Results indicate that the new bimaterial thermal expansion method is accurate within 15%-20% of the actual cantilever spring constant, which is comparable to other nondestructive calibration techniques. PMID:19044356
Nagal, K.; Yamaguchi, T.
1995-11-01
This paper presents numerical solutions for the chaotic oscillations of a shallow cylindrical shell. The shell having a circular cylindrical surface and a rectangular boundary is excited by periodic acceleration laterally. The Donnell equations modified with the transverse inertia force are used. The basic equation is reduced to the nonlinear differential equation of a multiple-degree-of-freedom system by the Galerkin procedure. The fundamental characteristics are found for the shell of a square boundary and of all boundaries simply supported. The time progresses of the chaotic responses are investigated by the numerical integration by the Runge-Kutta-Gill method. The chaotic response is identified by the Lyapunov exponent and the Poincare projection onto the phase space. The Lyapunov dimension is examined by changing the assumed modes of vibration.
Feasibility study of a Ka-/Ka-band dichroic plate with stepped rectangular apertures
NASA Technical Reports Server (NTRS)
Chen, J. C.
1993-01-01
For the Cassini spacecraft mission, a dichroic plate is needed to pass Ka-band uplink (34.2 to 34.7 GHz) and to reflect Ka-band downlink (31.8 to 32.3 GHz) for dual-frequency operation in the Deep Space Network. The special characteristic of the Ka-/Ka-band dichroic plate is that the pass band and the reflective band are only 1.9 GHz (5.7 percent) apart. A thick dichroic plate with stepped rectangular apertures that function as resonator filters was chosen for the Ka-/Ka-band dichroic plate design. The results of the feasibility study are presented in this article.
Laser velocimeter and total pressure measurements in circular-to-rectangular transition ducts
NASA Technical Reports Server (NTRS)
Patrick, William P.; Mccormick, Duane C.
1988-01-01
A comprehensive set of total pressure and three-component laser velocimetry (LV) data were obtained within two circular-to-rectangular transition ducts at low subsonic speeds. This set of reference data was acquired for use in identifying secondary flow mechanisms and for assessing the accuracy of computational procedures for calculating such flows. Data were obtained at the inlet and exit planes of an aspect ratio three duct having a length-to-diameter ratio of one (AR310) and an aspect ratio six duct having a length-to-diameter ratio of three (AR630). Each duct was unseparated throughout its transition section. It is therefore concluded that secondary flows can play an important part in the fluid dynamics of transition ducts and needs to be addressed in computational analysis. The strength of the secondary flows depends on both the aspect ratio and relative axial duct length.
Magnetic vortex-antivortex dynamics on a picosecond timescale in a rectangular Permalloy pattern
Kim, D.-H.; Mesler-Lai, B.; Anderson, E.; Fischer, P.; Moon, J.-H.; Lee, K.-J.
2009-06-25
We report our experimental finding that there exists a pair of magnetic vortex and antivortex generated during an excited motion of a magnetic vortex core. Two vortices structure in 2 x 4 {micro}m{sup 2} rectangular Permalloy pattern is excited by an external field pulse of 1-ns duration, where each vortex is excited and followed by the vortex core splitting. X-ray microscopy with high spatiotemporal resolution enables us to observe a linking domain between two temporarily generated pairs of vortex-antivortex cores only surviving for several hundreds of picoseconds. The linking domain structure is found to depend on the combinational configuration of two original vortex cores, which is supported by micromagnetic simulations with a very good agreement.
Noise transmission loss of a rectangular plate in an infinite baffle
NASA Technical Reports Server (NTRS)
Roussos, L. A.
1985-01-01
An improved analytical procedure was developed that allows for the efficient calculation of the noise transmission characteristics of a finite rectangular plate. Both isotropic and symmetrically laminated composite plates are considered. The plate is modeled with classic thin-plate theory and is assumed to be simply supported on all four sides. The incident acoustic pressure is assumed to be a plane wave impinging on the plate at an arbitrary angle. The reradiated pressure is assumed to be negligible compared with the blocked pressure, and the plate vibrations are calculated by a normal-mode approach. A Green's function integral equation is used to link the plate vibrations to be transmitted far-field sound waves, and transmission loss is calculated from the ratio of incident to transmitted acoustic powers. The result is a versatile research and engineering analysis tool that predicts noise transmission loss and enables the determination of the modal behavior of the plate.
NASA Astrophysics Data System (ADS)
Wu, Tiesheng; Liu, Yumin; Yu, Zhongyuan; Ye, Han; Peng, Yiwei; Shu, Changgan; Yang, Chuanghua; Zhang, Wen; He, Huifang
2015-03-01
A surface plasmon polaritons (SPPs) temperature sensor which consists of two metal-insulator-metal (MIM) waveguides coupled to each other by an ethanol-sealed rectangular cavity is proposed. The transmission characteristics of the nanodevice are theoretically analyzed and numerically simulated by two-dimension finite difference time domain (FDTD) method. The temperature sensing characteristics of the SPPs waveguide sensor are systematically analyzed by investigating the transmission spectra. The results indicate that the position of the transmission peak wavelengths has a linear relationship with the ambient temperature. The temperature sensitivity increases with the increase of the cavity length and decrease of the cavity height. The temperature sensitivity of the nanometeric sensor can reach as high as -0.65 nm/°C. It could be utilized to develop ultracompact temperature sensor for high integration.
Broadband sound attenuation on a periodic array of rectangular profile holes in plate
NASA Astrophysics Data System (ADS)
Moiseyenko, R. P.; Pennec, Y.; Marchal, R.; Bonello, B.; Djafari-Rouhani, B.
2014-04-01
Transmission of acoustic waves through a periodic array of sub-wavelength slits or holes have been studied in several recent works in relation with physical phenomena such as resonant (extraordinary) transmission, broadband sound shielding or acoustic induced transparency (AIT). In this work, we present for the first time the study of analogous phenomena for Lamb waves propagating in a thin plate. We study the transmission through one or two rows of a periodic array constituted by thin bridges separated by rectangular holes. When two rows of such an array are considered, the choice of the distance between both rows allows the realization of a broadband attenuation up to 99% in the transmission. These investigations should have implications for sound isolation, filtering and sensing applications.
Performance and rotor loads measurements of the Lynx XZ170 helicopter with rectangular blades
NASA Technical Reports Server (NTRS)
Lau, Benton H.; Louie, Alexander W.; Griffiths, Nicholas; Sotiriou, Costantinos P.
1993-01-01
This report presents the results of a series of flight tests on the Lynx XZ170 helicopter with rectangular blades. The test objectives were to explore the flight envelope and to measure the performance and structural loads of the Lynx main-rotor system. The tests were conducted as part of the British Experimental Rotor Program (BERP) under a contract with the Ministry of Defense in England. Data were acquired for steady-level flights at five weight coefficients. Some flight conditions were tested at beyond the retreating-blade stall boundary, which was defined by a predetermined limit on the pitchlink vibratory load. In addition to documenting the flight conditions and data, this report describes the aircraft, particularly the rotor system, in detail.
Study of the far wake vortex field generated by a rectangular airfoil in a water tank
NASA Technical Reports Server (NTRS)
Lezius, D. K.
1973-01-01
Underwater towing experiments were carried out with a rectangular airfoil of aspect ratio 5.3 at 4 and 8 deg angles of attack and at chord-based Reynolds numbers between 2 x 100,000 and 7.5 x 100,000. Quantitative measurements by means of the hydrogen bubble technique indicated lower peak swirl velocities in the range of 100 to 1000 lenghts downstream than have been measured in wind tunnel of flight tests. The maximum circumferential velocity decayed whereas the turbulent eddy viscosity increased. This behavior and other known rates of vortex decay are explained in terms of an analytical solution for the vortex problem with time varying eddy viscosity. It is shown that this case corresponds to nonequilibrium turbulent vortex flow.
Liu, Chao; Hu, Guoqing; Jiang, Xingyu; Sun, Jiashu
2015-02-21
Inertial microfluidics has emerged as an important tool for manipulating particles and cells. For a better design of inertial microfluidic devices, we conduct 3D direct numerical simulations (DNS) and experiments to determine the complicated dependence of focusing behaviour on the particle size, channel aspect ratio, and channel Reynolds number. We find that the well-known focusing of the particles at the two centers of the long channel walls occurs at a relatively low Reynolds number, whereas additional stable equilibrium positions emerge close to the short walls with increasing Reynolds number. Based on the numerically calculated trajectories of particles, we propose a two-stage particle migration which is consistent with experimental observations. We further present a general criterion to secure good focusing of particles for high flow rates. This work thus provides physical insight into the multiplex focusing of particles in rectangular microchannels with different geometries and Reynolds numbers, and paves the way for efficiently designing inertial microfluidic devices. PMID:25563524
Density modification by two superposing TE{sub 10} modes in a plasma filled rectangular waveguide
Tomar, Sanjay K.; Malik, Hitendra K.
2013-07-15
Microwave and plasma interaction is examined via two fundamental TE{sub 10} modes propagating in a plasma filled rectangular waveguide after superposing at a smaller angle. The propagation of the resultant mode realized from these two modes is governed by a wave equation obtained using the Maxwell's equations. This equation is solved numerically using fourth order Runge-Kutta method for the field amplitude of the microwave in the waveguide considering the waveguide to be made up of a perfect conductor and filled with different types of initial plasma density distributions, viz. homogeneous density, linear density with gradient in the propagation direction, and the density with Gaussian profile along the waveguide width. A phenomenon similar to the duct formation by high power microwaves is found to take place, where the plasma density attains interesting profiles. These profiles can be controlled by the angle of superposition, phase difference between the fields of the two modes, microwave frequency and microwave field amplitude.
Unification of bosonic and fermionic Z2 spin liquids on a rectangular lattice
NASA Astrophysics Data System (ADS)
Chatterjee, Shubhayu; Steinberg, Julia; Sachdev, Subir
Recent theories have postulated the presence of a fractionalized Fermi liquid (FL*) in the pseudogap metal phase of cuprates. The FL* phase can be described as a spin liquid co-existing with fermionic charge carrying quasiparticles. Underdoped cuprates also show a variety of competing orders, including nematic order which reduce the C4 symmetry of the square lattice to C2. Motivated by this, we classify mean-field bosonic spin liquids on a rectangular lattice using projective symmetry groups (PSG), and find equivalent descriptions in terms of fermionic partons. In particular, we find a fermionic spin liquid ansatz corresponding to a bosonic Z2 spin liquid with favorable mean field energy. The fermionic ansatz might be useful to investigate the transition from a FL* to a fermi liquid.
Tracing the buckling of a rectangular plate with the Block GMRES method
NASA Astrophysics Data System (ADS)
Chien, C.-S.; Chang, S.-L.; Mei, Z.
2001-11-01
We investigate bifurcation scenario of the von Kármán equations with partially clamped boundary conditions defined in rectangular domains. First, we study how the (preconditioned) Block GMRES method can be used in the context of continuation methods for tracing solution curves of large systems of nonlinear equations. Next, we discuss linear stabilities of the von Kármán equations with partially clamped boundary conditions. In particular, we calculate the first seven eigenvalues and its associated eigenfunctions of the linearized von Kármán equations via computer algebra. The Block GMRES method is used to solve linear systems and to detect singularity along solution paths of the discrete problem. Sample numerical results are reported.
LDV measurement and Navier-Stokes computation of parallel jet mixing in a rectangular confinement
Kunz, R.F.; D`Amico, S.W.; Vassallo, P.F.; Zaccaria, M.A.; Aksoy, H.; So, R.M.C.
1995-06-01
Laser Doppler Velocimetry (LDV) measurements were taken in a rectangular confinement into which issues a row of parallel jets. Two-component measurements were taken with two optics orientations yielding three mean velocity components and four Reynolds stress components. As observed in isolated three dimensional wall bounded jets, the transverse diffusion of the jets is quite large. The data indicates that this rapid mixing process is due to strong secondary flows, transport of large inlet intensities and Reynolds stress anisotropy effects. Navier-Stokes analyses of this configuration underpredict the rate of transverse jet diffusion. Detailed numerical accuracy studies show that this is attributed to shortcomings in low-Reynolds number two-equation turbulence modelling. A low-Reynolds number full-Reynolds stress model is shown to provide improvement.
Transport ac loss in a rectangular thin strip with power-law E (J) relation
NASA Astrophysics Data System (ADS)
Li, Shuo; Chen, Du-Xing; Fan, Yu; Fang, Jin
2015-01-01
Transport ac losses of a rectangular thin strip obeying relation E /Ec =(J /Jc) n with a fixed critical current Ic and n = 5, 10, 20, 30 , and 40 are accurately computed at a fixed frequency f as functions of the current amplitude Im . The results may be interpolated and scaled to those at any values of Ic, f , and 5 ⩽ n ⩽ 40 . Normalized in the same way as that in Norris' analytical formula derived from the critical-state model and converting f to a critical frequency fc , the modeling results may be better compared with the Norris formula and experimental data. A complete set of calculated modeling data are given with necessary formulas to be easily used by experimentalists in any particular case.
Quasi suppression of higher-order diffractions with inclined rectangular apertures gratings
Liu, Yuwei; Zhu, Xiaoli; Gao, Yulin; Zhang, Wenhai; Fan, Quanping; Wei, Lai; Yang, Zuhua; Zhang, Qiangqiang; Qian, Feng; Chen, Yong; He, Weihua; Wu, Yinzhong; Yan, Zhuoyang; Hua, Yilei; Zhao, Yidong; Cui, Mingqi; Qiu, Rong; Zhou, Weimin; Gu, Yuqiu; Zhang, Baohan; Xie, Changqing; Cao, Leifeng
2015-01-01
Advances in the fundamentals and applications of diffraction gratings have received much attention. However, conventional diffraction gratings often suffer from higher-order diffraction contamination. Here, we introduce a simple and compact single optical element, named inclined rectangular aperture gratings (IRAG), for quasi suppression of higher-order diffractions. We show, both in the visible light and soft x-ray regions, that IRAG can significantly suppress higher-order diffractions with moderate diffraction efficiency. Especially, as no support strut is needed to maintain the free-standing patterns, the IRAG is highly advantageous to the extreme-ultraviolet and soft x-ray regions. The diffraction efficiency of the IRAG and the influences of fabrication constraints are also discussed. The unique quasi-single order diffraction properties of IRAG may open the door to a wide range of photonic applications. PMID:26563588
Geng, Qian; Li, Huan; Li, Yueming
2014-05-01
Experiments were performed to investigate the vibration and acoustic response characteristics of a clamped rectangular aluminum plate in thermal environments. Modal tests were carried out to study the influence of thermal environment on natural vibration. With the increment of structural temperature, natural frequencies of the plate decrease obviously. Mode shape interchange was observed for the modes with frequencies very close to each other. The thermally induced softening effect has unequal influences on the plate along the two in-plane directions. Numerical methods were also employed to study the experimental phenomena. Calculated results indicated that the initial deflection has a great influence on the natural vibration of the heated plate. Even a slight curvature can reduce the thermally induced softening effect obviously. Dynamic response tests were carried out under acoustic and mechanical excitations, and the measured results indicate that the variation in damping determines the response amplitudes at resonant peaks in the test. PMID:24815251
Convergence of intense aerial acoustic waves radiated by a rectangular transverse vibrating plate
NASA Astrophysics Data System (ADS)
Nakai, Tomoki; Asami, Takuya; Miura, Hikaru
2016-07-01
A stripe-mode rectangular transverse vibrating plate can be used as a sound source that emits intense ultrasonic waves in air by placing a jut driving point outside the vibrating plate. The aim of this research was to use this vibrating plate to focus sound waves in the direction perpendicular to the nodal lines of the vibrating plate, which differs from the conventional direction. In this study, we investigated new methods for focusing the emitted sound waves by arranging reflective plates around the vibrating plate, using a design equation for each node between nodes in the vibrating plate, and placing additional reflective plates at an outer position beyond the convergence point, and found that a powerful acoustic field can be formed at an arbitrary position.
Buckling tests of a 10 foot diameter stiffened cylinder with rectangular cutouts
NASA Technical Reports Server (NTRS)
Davis, Randall C.; Carder, Fred
1987-01-01
A 10-foot diameter aluminum cylinder with rectangular cutouts in its ring and stringer stiffened wall was loaded to failure by an end bending moment. A 24x27 inch cutout, centered on the compression side of the shell, was first cut into the cylinder. After testing, the cutout area was enlarged to a 36/36 inch square cutout that removed the material damaged by buckling during the first test. After the second buckling test, the cutout area was patched with an equivalent stiffness plate bolted over the cutout hole. The cylinder was rotated 120 deg. and a 18x18 inch square hole cut into the center of the new compression side of the shell. Test specimen details, test procedures, and test results are presented.
Analysis of Mirnov signals from coils mounted in a rectangular array
Navarro, A P; Dunlap, J L; Pare, V K; Burris, R D
1980-01-01
Data analysis techniques for determining the structure of MHD instabilities in the ISX-B tokamak from Mirnov signals have been under development. Standard techniques cannot be applied directly in this case since the rectangular shape of the vacuum chamber requires a similar shape for the poloidal array of magnetic pickup coils. Components of the poloidal field perturbation are considered both parallel and perpendicular to the chamber walls and a twofold problem is addressed: (a) determining the relative signal phases as a function of poloidal angle along the array for any particular poloidal structure of plasma perturbation, without boundary effects; and (b) determining distortions of these phase lines due to eddy currents in the chamber. Results from simulation of plasma perturbations and from ISX-B experimental data are discussed.
Lee, Dukhyung; Kim, Dai-Sik
2016-01-01
We study light scattering off rectangular slot nano antennas on a metal film varying incident polarization and incident angle, to examine which field vector of light is more important: electric vector perpendicular to, versus magnetic vector parallel to the long axis of the rectangle. While vector Babinet's principle would prefer magnetic field along the long axis for optimizing slot antenna function, convention and intuition most often refer to the electric field perpendicular to it. Here, we demonstrate experimentally that in accordance with vector Babinet's principle, the incident magnetic vector parallel to the long axis is the dominant component, with the perpendicular incident electric field making a small contribution of the factor of 1/|ε|, the reciprocal of the absolute value of the dielectric constant of the metal, owing to the non-perfectness of metals at optical frequencies. PMID:26740335
Application of rectangular and elliptical dielcore feed horns to elliptical reflector antennas
NASA Astrophysics Data System (ADS)
Lier, Erik; Rahmat-Samii, Yahya; Rengarajan, Sembiam R.
1991-11-01
The pattern characteristics of elliptical reflector antennas are investigated when they are fed by rectangular and elliptical horns partially filled with a dielectric. The bandwidth characteristics of these dielcore horns are superior to those of their corrugated horn counterparts. Representative reflector patterns are computed to properly demonstrate the utility of these feeds for reflector antennas with elliptical apertures. This reflector antenna exhibits high efficiency and low cross polarization, and may be suitable for radar and satellite antenna applications. The antenna configuration may become useful in relatively small antennas where more than 10 percent cross-polar bandwidth is required. The efficient dielcore horns may also be used as feeds for elliptical nonshaped dual-reflector antennas.
Design and Fabrication of Broadband Graded Ultrasonic Transducers with Rectangular Kerfs
Guo, Hongkai; Cannata, Jonathan M.; Zhou, Qifa; Shung, K. Kirk
2005-01-01
Broadband ultrasound imaging is capable of achieving superior resolution in clinical applications. An effective and easy way of manufacturing broadband transducers is desired for these applications. In this work, a graded material in which the piezoelectric plate is mechanically graded with rectangular grooves is introduced. Finite Element Analysis (FEA) demonstrated that the graded piezoelectric material could achieve a broadband time-domain response resulted from multiple resonant modes. Experimental tests were carried out to validate these theoretical results. Based upon the FEA designs, several single-element transducers were fabricated using either a non-diced ceramic or a diced graded ceramics. A superior bandwidth of 92% was achieved by the graded transducer when compared to a bandwidth of 56% produced by the non-diced ceramic transducer at the expense of a reduced sensitivity. PMID:16422423
Impact of nonlinear absorption on propagation of microwave in a plasma filled rectangular waveguide
NASA Astrophysics Data System (ADS)
Sobhani, H.; Vaziri, M.; Rooholamininejad, H.; Bahrampour, A. R.
2016-07-01
In collisional and ponderomotive predominant regimes, the propagation of microwave in rectangular waveguide filled with collisional plasma is investigated numerically. The dominant mode is excited through an evacuated waveguide and then enters a similar and co-axis waveguide filled with plasma. In collisional predominant regime, the amplitude of electric field is oscillated along propagation path; outset of propagation path due to the electron-ion collision, the intensity oscillations are reduced. Afterward, under competition between the collisional nonlinearity and absorption, the intensity is increased, so the electron density peak is created in middle of waveguide. In ponderomotive predominant regime, the intensity is slowly decreased due to collision, so the electron density is ramped. Control parameters, like the frequency, input power, collision frequency, and background electron density are surveyed that can be used to control propagation characteristics of microwave. This method can be used to control heating of fusion plasma and accelerate charged particle.
A nongray analysis of radiating-convecting rectangular plate-fin arrays
NASA Astrophysics Data System (ADS)
Elazhary, A. M.; Soliman, H. M.
2008-02-01
A complete analysis of heat transfer in rectangular fin arrays has been conducted taking into consideration convection and radiation at all surfaces, as well as radiative exchange between the fins and all neighboring surfaces. The analysis assumes diffuse nongray surfaces and uses the spectral optical properties of stainless steel AISI 430. Three different gray models were proposed in order to assess the effect of the gray assumption on the heat-transfer characteristics. Results are presented for the temperature and radiative-flux distributions along the fin, the radiative flux along the base, the contribution of the radiative component to the overall heat transfer, and the effectiveness of the fin array. Significant deviations in some of these results were found between the nongray model and the gray models. In general, convection was found to be the more effective mode of heat transfer in fin arrays and the effectiveness of the array decreases as the contribution of the radiative component increases.
An experimental investigation of the flow field of a rectangular wall jet
NASA Technical Reports Server (NTRS)
Horne, C.; Karamcheti, K.
1979-01-01
The structure of a laminar, rectangular wall jet developing from an initially parabolic velocity profile was investigated with measurements of the mean and fluctuating velocity field, and with Schlieren flow visualization. The effects on mean and fluctuating velocity fields of changes in the jet Reynolds number over the range of from 0 to 4800, and of various wall lengths ranging from 0 to 312 jet widths were studied. For a given wall length and Reynolds number, disturbances in the flow field were regular and periodic, and of a constant frequency in a large region of the flow field. Small, self-excited disturbances at the nozzle exit were observed to grow exponentially with downstream distance, and roll up to form a convecting array of discrete vortices. For certain values of wall length and jet speed, discrete audible tones were detected, and appeared to be associated with an enhancement of the regularity and stability of the vortex array.
Use of Rectangular Capillary Chambers for Nondestructive Microscopic Observation of Biofilm on Sand
NASA Astrophysics Data System (ADS)
Ochiai, N.; Dragila, M.; Parke, J.
2005-12-01
Slow sand filter removal of bacterial and fungal pathogens from water has been shown to depend on development of biofilms on sand near the filter surface. Over time, hydraulic conductivity of slow sand filters is considerably reduced, presumably due to excessive biofilm development or plugging of surface pores by particulate matter. Microscopic observation of biofilms in porous media typically requires destructive sampling of media or use of micromodels to simulate pore systems. We are developing a flow-thru chamber consisting of a thin-walled rectangular capillary attached to a mount that can be manipulated with a conventional microscope stage. Capillaries are easily packed with granular media and allow continuous, non-destructive observation of pore systems over time. Initial trials using epi-fluorescence microscopy demonstrate the potential to monitor biofilm development on pore faces or adsorption of particulate matter at the water-solid or air-water interface.
Characteristics of Turbulent Flow Past Passive Rectangular Cavity at Large Reynolds Numbers
NASA Astrophysics Data System (ADS)
Ezhil Kumar, Perumal Kumaresan; Mishra, Debi Prasad
2016-06-01
In the present investigation, turbulent flow past passive rectangular cavity is investigated numerically for four mainstream Reynolds numbers namely Re ms = 20,000-50,000. Validation study reveals that the numerical models used in the present investigation predicts the data close to the existing experimental results. Further attempts are made to bring out the flow structure in terms of velocity profile, velocity gradients, shear layer growth rate, and turbulence characteristics. Numerical results are analyzed to bring out the variation in the velocity profile at different axial locations within the cavity. Also, the velocity gradient, turbulence level at the shear layer and the reverse flow velocity in the cavity are found to be sensitive to the mainstream Reynolds number. Finally, the cavity drag is estimated and its relation to the pressure drop across the cavity is brought out. These results reveal the nature of interaction between the passive cavity flow and mainstream flow.
NASA Technical Reports Server (NTRS)
1985-01-01
The electrophoretic mobility of a cell in solution is defined by its velocity divided by the electric field strength it experiences. An obvious way to measure the mobility of cells is to apply a constant electric field to a suspension of cells in a glass chamber and clock the velocities of individual cells through a microscope. This microscope method is the classic technique in cell electrophoresis and it has been used for the bulk of research in this field. Two aspects of the microscope method can critically affect the accuracy and consistency of its cell mobility measurements: (1) the electroosmotic fluctuations in the chamber from measurement to measurement; and (2) the number of cells which can be practically measured for statistically meaningful results. A new method of analyzing microelectrophoretic data using a computer program has been developed which addresses both of these aspects. It makes possible the mobility measurements of individual cells as positions throughout the rectangular chamber depth during asymmetric electroosmotic flow.
NASA Astrophysics Data System (ADS)
Grigoryeva, N. Yu.; Popov, D. A.; Kalinikos, B. A.
2014-09-01
A theory has been constructed that strictly describes the spectrum of dipole-exchange spin waves in an arbitrarily magnetized anisotropic ferrite waveguide with a rectangular cross section. The theory takes into account the spatial inhomogeneity of the internal magnetic field in the waveguide cross section. The influence of parameters of the ferrite waveguide on the distribution of the internal magnetic field in the waveguide cross section is analyzed. The dispersion characteristics of two waveguide types most widely used in practice are investigated. The dipole-exchange spin wave spectra calculated for a transversely magnetized waveguide are presented and the distributions of the dynamic magnetization in the waveguide cross section for several types of volume and localized spin-wave modes are constructed.
NASA Technical Reports Server (NTRS)
Ko, William L.
1994-01-01
The combined load (mechanical or thermal load) buckling equations were established for orthotropic rectangular sandwich panels under four different edge conditions by using the Rayleigh-Ritz method of minimizing the total potential energy of a structural system. Two-dimensional buckling interaction curves and three-dimensional buckling interaction surfaces were constructed for high-temperature honeycomb-core sandwich panels supported under four different edge conditions. The interaction surfaces provide overall comparison of the panel buckling strengths and the domains of symmetrical and antisymmetrical buckling associated with the different edge conditions. In addition, thermal buckling curves of these sandwich panels are presented. The thermal buckling conditions for the cases with and without thermal moments were found to be identical for the small deformation theory.
NASA Astrophysics Data System (ADS)
Wang, Yue; Tong, Yijing; Zhang, Xin
2016-04-01
Transmission spectra of terahertz waves through a two-dimensional array of asymmetric rectangular apertures on super-aligned multi-walled carbon nanotube films were obtained experimentally. In this way, the anisotropic transmission phenomena of carbon nanotube films were observed. For a terahertz wave polarization parallel to the orientation of the carbon nanotubes and along the aperture short axis, sharp resonances were observed and the resonance frequencies coincided well with the surface plasmon polariton theory. In addition, the minima of the transmission spectra were in agreement with the location predicted by the theory of Wood's anomalies. Furthermore, it was found that the resonance profiles through the carbon nanotube films could be well described by the Fano model.
Effect of Thermal Gradient on Vibration of Non-uniform Visco-elastic Rectangular Plate
NASA Astrophysics Data System (ADS)
Khanna, Anupam; Kaur, Narinder
2016-04-01
Here, a theoretical model is presented to analyze the effect of bilinear temperature variations on vibration of non-homogeneous visco-elastic rectangular plate with non-uniform thickness. Non-uniformity in thickness of the plate is assumed linear in one direction. Since plate's material is considered as non-homogeneous, authors characterized non-homogeneity in poisson ratio and density of the plate's material exponentially in x-direction. Plate is supposed to be clamped at the ends. Deflection for first two modes of vibration is calculated by using Rayleigh-Ritz technique and tabulated for various values of plate's parameters i.e. taper constant, aspect ratio, non-homogeneity constants and thermal gradient. Comparison of present findings with existing literature is also provided in tabular and graphical manner.
Magnetic field effects on THz radiation from rectangular shape Bi2212 IJJ’s
NASA Astrophysics Data System (ADS)
Yamaki, Kazuhiro; Tsujimoto, Manabu; Yamamoto, Takashi; Minami, Hidetoshi; Kadowaki, Kazuo
2010-12-01
The effects of magnetic field on terahertz radiation emitted from the rectangular mesa of intrinsic Josephson junctions (IJJ’s) made of Bi2212 single crystals were studied up to 150 Oe. Strong suppression of the radiation power was observed when magnetic field was applied to the c-axis of the sample, while in the case of H//ab-plane, the radiation power showed a weak and broad peak in the weak field region (˜50 Oe), then it decreased and diminished around 150 Oe. These magnetic field effects are interpreted by the strong influence of magnetic field on the I-V curve, which set up the condition for the THz radiation.
Microwave breakdown for the TE{sub 10} mode in a rectangular waveguide
Malik, Hitendra K.; Aria, Anil K.
2013-08-15
Microwave breakdown is studied for the lowest order TE{sub 10} mode in a rectangular waveguide with the help of direct variational approach via the continuity equation along with the use of ionisation and attachment frequency. We investigate the role of the ionisation, attachment of electron with neutral gas or air molecules and the diffusion on microwave breakdown threshold in the waveguide filled with air or Ar Gas. We examine the effect of different gases and microwave parameters on the diffusion length and the breakdown threshold of electric field of continuous microwave and pulsed microwave. We also employ numerical approach for obtaining the results and compare them with the ones of variational approach.
Slow light generation in single-mode rectangular core photonic crystal fiber
NASA Astrophysics Data System (ADS)
Yadav, Sandeep; Saini, Than Singh; Kumar, Ajeet
2016-05-01
In this paper, we have designed and analyzed a rectangular core photonic crystal fiber (PCF) in Tellurite material. For the designed photonics crystal fiber, we have calculated the values of confinement loss and effective mode area for different values of air filling fraction (d/Λ). For single mode operation of the designed photonic crystal fiber, we have taken d/Λ= 0.4 for the further calculation of stimulated Brillouin scattering based time delay. A maximum time delay of 158 ns has been achieved for input pump power of 39 mW. We feel the detailed theoretical investigations and simulations carried out in the study have the potential impact on the design and development of slow light-based photonic devices.
Lee, Dukhyung; Kim, Dai-Sik
2016-01-01
We study light scattering off rectangular slot nano antennas on a metal film varying incident polarization and incident angle, to examine which field vector of light is more important: electric vector perpendicular to, versus magnetic vector parallel to the long axis of the rectangle. While vector Babinet’s principle would prefer magnetic field along the long axis for optimizing slot antenna function, convention and intuition most often refer to the electric field perpendicular to it. Here, we demonstrate experimentally that in accordance with vector Babinet’s principle, the incident magnetic vector parallel to the long axis is the dominant component, with the perpendicular incident electric field making a small contribution of the factor of 1/|ε|, the reciprocal of the absolute value of the dielectric constant of the metal, owing to the non-perfectness of metals at optical frequencies. PMID:26740335
NASA Technical Reports Server (NTRS)
Gyekenyesi, J. P.; Mendelson, A.
1977-01-01
The line method of analysis is applied to the Navier-Cauchy equations of elastic equilibrium to calculate the displacement field in a finite geometry bar containing a variable depth rectangular surface crack under extensionally applied uniform loading. The application of this method to these equations leads to coupled sets of simultaneous ordinary differential equations whose solutions are obtained along sets of lines in a discretized region. Using the obtained displacement field, normal stresses, and the stress-intensity factor variation along the crack periphery are calculated for different crack depth to bar thickness ratios. Crack opening displacements and stress-intensity factors are also obtained for a through-thickness, center-cracked bar with variable thickness. The reported results show a considerable potential for using this method in calculating stress-intensity factors for commonly encountered surface crack geometries in finite solids