检索结果-南通市图书馆

Effect of cut-off frequency of Butterworth Filter on Detectability and Contrast of Hot and Cold Regions in Tc-99m SPECT

在线全文

学校读者我要写书评

暂无评论

International Journal of Medical Physics, Clinical Engineering and Radiation Oncology 2016年第1期5卷 100-109页

作者： Inayatullah Shah Sayed Nor Syahirah Mohamed Nasrudin Department of Diagnostic Imaging and Radiotherapy Kulliyyah (Faculty) of Allied Health Sciences International Islamic University of Malaysia Kuantan Malaysia

In SPECT, noise is one of the major limitations that degrade image quality. To suppress the noisy signals in an image, digital filters are most commonly applied. However, in SPECT image reconstruction, selection of an appropriate filter and its functions has always remained a difficult task. In this work an attempt was made to investigate the effects of varying cut-off frequencies and in keeping the order of Butterworth filter constant on detectability and contrast of hot and cold re-gions images. A new insert simulating hot and cold regions which provides similar views in a reconstructed image was placed in the phantom’s cylindrical source tank and imaged. Tc-99m radionuclide was distributed uniformly in the phantom. SPECT data were collected in a 20% energy window centered at 140 keV by a Philips ADAC Forte dual head gamma camera mounted with a LEHR collimator. Images were generated by using the filtered backprojection technique. A Butterworth filter of order 5 with cut-off frequencies 0.35 and 0.45 cycles·cm-1 was applied. Images were examined in terms of hot and cold regions, detectability and contrast. Results show that the hot and cold regions’ detectability and contrast vary with the change of cut-off frequency. With a 0.45 cycles·cm-1 cut-off frequency, a significant enhancement in contrast of cold regions was achieved as compared to a 0.35 cycles·cm-1 cut-off frequency. Furthermore, the detectability of hot and cold regions improved with the use of a 0.45 cycles·cm-1 cut-off frequency. In conclusion, image quality of hot and cold regions affected in a different way with a change of cut-off frequency. Thus, care should be taken in selecting the filter cut-off frequency prior to reconstruction of images;particularly, when both types of regions are expected in the reconstructed image.

关键词： Detectability SPECT Noise Image Quality cut-off frequency Mathematical Filters

Radio-frequency transistors from millimeter-scale graphene domains

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Chinese Physics B 2014年第11期23卷 470-475页

作者：魏子钧傅云义刘竞博王紫东贾越辉郭剑任黎明陈远富张酣黄如张兴 Institute of Microelectronics Peking University State Key Laboratory of Electronic Thin Films and Integrated Devices University of Electronic Science and Technology of China School of Physics Peking University

Graphene is a new promising candidate for application in radio-frequency （RF） electronics due to its excellent elec- tronic properties such as ultrahigh carrier mobility, large threshold current density, and high saturation velocity. Recently, much progress has been made in the graphene-based RF field-effect transistors （RF-FETs）. Here we present for the first time the high-performance top-gated RF transistors using millimeter-scale single graphene domain on a SiO2/Si substrate through a conventional microfabrication process. A maximum cut-off frequency of 178 GHz and a peak maximum os- cillation frequency of 35 GHz are achieved in the graphene-domain-based FET with a gate length of 50 nm and 150 nm, respectively. This work shows that the millimeter-scale single graphene domain has great potential applications in RF devices and circuits.

关键词： millimeter-scale graphene domain radio-frequency transistor cut-off frequency maximum oscil-lation frequency

Indium antimonide based HEMT for RF applications

在线全文

学校读者我要写书评

暂无评论

Journal of Semiconductors 2014年第11期35卷 20-22页

作者： T.D.Subash T.Gnanasekaran K.N.S.K College of Engineering Nagercoil-629901India RMK College of Engineering and Technology Tamil Nadu601206India

We report on an indium antimonide high electron mobility transistor with record cut-off frequency characteristics. For high frequency response it is important to minimize parasitic resistance and capacitance to improve short-channel effects. For analog applications adequate pinch-off behavior is demonstrated. For proper device scaling we need high electron mobility and high electron density. Toward this end, the device design features and simulation are carried out by the Synopsys TCAD tool. A 30 nm InSb HEMT exhibits an excellent cut-off frequency of 586 GHz. To the knowledge of the authors, the obtained cut-off frequency is the highest ever reported in any FET on any material system.

关键词： HEMT InSb gate length cut-off frequency short-channel effects

Performance Evaluation and Effectiveness of the Reverberation Room

在线全文

学校读者我要写书评

暂无评论

Sound & Vibration 2021年第1期55卷 43-55页

作者： Mohamed Abd-Elbasseer Hatem Kh Mohamed Acoustics Laboratory National Institute of Standards(NIS)GizaEgypt

This research presents a thorough evaluation of the reverberation room at Acoustics Laboratory in National Institute of Standards(NIS)according to the related international standards.The evaluation aims at examining the room performance and exploring its effectiveness in the frequency range from 125 Hz to 10000 Hz according to the international standard requirements.The room,which was designed and built several years ago,is an irregular rectangular shape free from diffusers.Its volume is about 158.84 m^(3),which meets the requirement of the ISO 354 standard Lmaxcut-off frequencies of one and one-third octave are 63 Hz and 100 Hz respectively;however Schroder frequency is 400 Hz.Calculations of cut-off frequency and modal density showed adequate modes that give acceptable uniformity starting comfortably from frequency of 125 Hz.The room has a reverberation time that is suitable for its size over the frequency range of interest.The room sound absorption surface area and its sound absorption coefficient satisfy the criteria given in ISO 3741 and ISO 354.There is an accepted diffuse sound field inside the room due to the standard deviation of measured sound level,which is less than 1.5 dB over all the frequency range.The only exception was 125 Hz which may be due to a lack of diffusivity of the sound field at this frequency.The evaluation proves that the NIS reverberation room is in full agreement with the international standards,which in turns qualifies the room to host measurements inside without concerns.

关键词： Reverberation room cut-off frequency sound absorption spatial uniformity modal counts

FORCED WAVE PROPAGATION IN VISCOELASTIC CABLE WITH SMALL SAG

维普期刊数据库评论

在线全文

维普期刊数据库

学校读者我要写书评

暂无评论

Acta Mechanica Solida Sinica 2001年第2期14卷 147-154页

作者： Li Yinghui Jian Kailin~1 Gao Qing Yin Xuegang~1 (Department of Applied Mechanics and Engineering, Southwest Jiaotong University, Chengdu 610031, China) (1 State Key Laboratory of Mechanical Transmission, Chongqing University, Chongqing 400044, China) Dept. of Appl. Mechanics and Eng. Southwest Jiaotong University Chengdu 610031 China Stt. Key Lab. of Mech. Transmission Chongqing University Chongqing 400044 China

Based on the linear viscoelastic differential constitutive law andcable structural model, the coupled longitudinal-transverse wavesthat propagate along a viscoelastic cable with small curvature isinvesti- gated. A mathematical model is presented that describes thethree-dimensional nonlinear response of a vis- coelastic cable. Anasymptotic form of this model is obtained for the linear response ofcables having small equilibrium curvature.

关键词： viscoelastic cable small equilibrium curvature cut-off frequency

30 nm T-gate enhancement-mode InAIN/AIN/GaN HEMT on SiC substrates for future high power RF applications

在线全文

学校读者我要写书评

暂无评论

Journal of Semiconductors 2017年第8期38卷 22-27页

作者： P.Murugapandiyan S.Ravimaran J.William Research Scholar Faculty of Information and Communication EngineeringAnna University Department of Electrical and Computer Science M.A.M College of Engineering Department of Electronics and Communication Engineering M.A.M.College of Engineering and Technology

The DC and RF performance of 30 nm gate length enhancement mode （E-mode） InAlN/AIN/GaN high electron mobility transistor （HEMT） on SiC substrate with heavily doped source and drain region have been inves- tigated using the Synopsys TCAD tool. The proposed device has the features of a recessed T-gate structure, lnGaN back barrier and Al2O3 passivated device surface. The proposed HEMT exhibits a maximum drain current density of 2.1 A/mm, transconductance gm of 1050 mS/mm, current gain cut-off frequency f of 350 GHz and power gain cut-off frequency fmax of 340 GHz. At room temperature the measured carrier mobility （μ）, sheet charge carrier density （ns） and breakdown voltage are 1580 cm2/（V.s）, 1.9× 1013 cm-2, and 10.7 V respectively. The superla- tives of the proposed HEMTs are bewitching competitor or future sub-millimeter wave high power RF VLSI circuit applications.

关键词： HEMT back-barrier recessed gate cut-off frequency regrown ohmic contact short channel effects

Design and Realization of Schottky Barrier Didoes in 130nm CMOS Process

在线全文

学校读者我要写书评

暂无评论

Journal of Beijing Institute of Technology 2017年第2期26卷 223-227页

作者： Junyu Shi Dasheng Cui Haidong Hao Haixia Wu Xin Lyu School of Information and Electronics Beijing Institute of Technology Beijing 100081 China

A polysilicon separated CMOS Schottky barrier diode is designed and tested in this study.By replacing the shallow trench isolation（STI）of a ploy ring,the series resistances of Schottky diodes are reduced,leading to an improvement in cut-off frequencies.The device structure is detailed and a device model is developed.Our analysis on the device shows that the cut-off frequency increases with the decreasing of the Schottky contact area.Based on this observation,the Schottky contact area is set to0.38×0.38μm^2,which is the minimum contact diffusion area allowed by the process flow.The distance between the anode and the cathode is also discussed.Diodes with different dimensions are fabricated and measured.Through extensive measurements,the optimum dimensions are obtained.Bondpads with a reduced area are used to improve the measurement accuracy.The measurement results show that these diodes can achieve a cut-off frequency of 1.5 THz.Thus,it is possible to use these diodes in THz detection.

关键词： Schottky barrier diodes cut-off frequency silicon THz detection

Analysis and performance exploration of high performance(HfO_2) SOI FinFETs over the conventional(Si_3N_4) SOI FinFET towards analog/RF design

在线全文

学校读者我要写书评

暂无评论

Journal of Semiconductors 2018年第12期39卷 68-74页

作者： Neeraj Jain Balwinder Raj VLSI Design Lab Department of Electronics and Communication Engineering Dr.B.R.Ambedkar National Institute of Technology (NIT)

Nowadays FinFET devices have replaced the MOS devices almost in all complex integrated circuits of electronic gadgets like computer peripherals, tablets, and smartphones in portable electronics. The scaling of FinFET is ongoing and the analog/RF performance is most affected by increased SCEs(short channel effects) in sub22 nm technology nodes. This paper explores the analog/RF performance study and analysis of high performance device-D2(conventional Hf02 spacer SOI FinFET) and device-D3(source/drain extended Hf02 spacer SOI FinFET) over the device-D1(conventional Si3 N4 spacer SOI FinFET) at 20 nm technology node through the 3-D(dimensional) simulation process. The major performance parameters like I(ON current), I(off current), gm(transconductance), gd(output conductance), A(intrinsic gain), SS(sub-threshold slope), TGF = g/I(trans-conductance generation factor), VEA(early voltage), GTFP(gain trans-conductance frequency product), TFP(tansconductance frequency product), GFP(gain frequency product), and f(cut-off frequency) are studied for evaluating the analog/RF performance of different flavored SOI FinFET structures. For analog performance evaluation,device-D3 and D2 give better results in terms of gm, ID(drain current) and SS parameters, and for RF performance evaluation device-D1 is better in terms of f, GTFP, TFP, and GFP parameters both at low and high values of V=0.05 V and V=0.7 V respectively.

关键词： SOI FinFET SCEs intrinsic gain trans-conductance cut-off frequency

On the Spectral Moments of Wind Waves

在线全文

学校读者我要写书评

暂无评论

China Ocean Engineering 2002年第1期17卷 135-140页

作者： LI Luping(李陆平) HUANG Peiji(黄培基) First Institute of Oceanography State Oceanic Adminustration Qingdao 266061 China First Institute of Oceanography State Oceanic Adminustration Qingdao 266061 China

In order to obtain high order spectral moments, the residual moment M(w(n))(i) = integral(0)(wn) w(i)S(w)dw, as proposed by Denis s, is presented for approximate estimation of spectral moment m(i) = integral(0)(infinity) w(i)S(w)dw. Glazman's partial averaging idea is discussed. It is pointed out that Glazman's method and definition of non-dimensional spectral moment can not be used to estimate spectral moments for engineering purposes and that method is not supported by theory and computation. The non-dimensional spectral moment of PM spectrum, which should be expressed as [GRAPHICS] is related to wind speed. The 0 - 8th moments of PM spectrum are estimated for wind speeds of 10, 20 and 30 m/s and some discussions are given.

关键词： spectral moment high order moment residual moment cut-off frequency