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1.
Thepostalservicestructurereferstothestatus,whichisoftenrepresentedbytheproportionofacertainserviceamongthewholerevenues,andtherelationshipofvariouspostalserviceswithinthecon textoftheservicestructure.Thechangingpostalenvironmentleadstosomechangesintheservicestructure.Thefollowingpartofthepaperwillreviewthelawofitsdevelopmentandmakesananalysisofitscurrentcharacteristics,andtheexistingproblems .1 TheLawoftheDevelopmentoftheServiceStructure  Fromthelate 1 980stotheendoflastcentury ,greatchan…  相似文献   

2.
An authentication code can be constructed with a family of ε-Almost strong universal (ε-ASU) hash functions, with the index of hash functions as the authentication key. This paper considers the performance of authentication codes from ε-ASU, when the authentication key is only partially secret. We show how to apply the result to privacy amplification against active attacks in the scenario of two independent partially secret strings shared between a sender and a receiver.  相似文献   

3.
A causal realization of an inverse system can be unstable, and an anti-causal realization is used to deal with this problem to provide a numerically stable procedure to realize the inverse system and compute its input signal. In this paper, we consider the anti-causal realization of the inverse of discrete-time linear periodic systems obtained by an outer-inner factorization approach. It presents an analysis and understanding of the inverse system error caused by different parts of the system components. The analysis shows that the inverse system error due to the mismatching of the system initial state in the anti-causal inverse system is inevitable in practical computations.  相似文献   

4.
1 IntroductionWiththedevelopmentandprosperityofthena tionaleconomy ,people’sneedsforthepostalser viceswillalsobegreatlyincreased .Therefore,theeconomicfactorswillplaythemostfundamentalandimportantroleinthedevelopmentofthemodernpostalservice.Inordertoknow…  相似文献   

5.
Historically ,scientiststriedtodevelopatheorytoexplainthemotivesofhumanbehavior.“Needs”havebeenregardedasabasisforstudyinghumanmotivesandevenasastartingpointofrealizingman sbehavior.ItwasMaslow ,masterofhumanis ticpsychology ,thatbegantoarrangetheclassifica tionorderofhumanneeds.However,heneverputqualitativeandquantitativeresearchestogether,butreliedontheobservationbyexperienceandpsycho logicalanalysis.Theauthoronceofferedhispointonclassificationofneedsbasedonthecharacteristicsoftradingandr…  相似文献   

6.
The PIN diode is an especial charge controldevice. The middle zone of a PIN diode between theheavily doped P-type semiconductor ( P ) and N-typesemiconductor ( N ) is so called region I with highresistivity, as shown in Fig.1. The region I of apractical PIN diode consists of the high resistivity Pmaterial called I(π)-type or high resistivity N materialcalled I(υ)-type. The density of carriers in the region Iis controlled mainly by the applied bias voltage.Therefore, the resistance o…  相似文献   

7.
An Analysis and Design of the Virtual Simulation Software Based on Pattern   总被引:1,自引:0,他引:1  
1 IntroductionVegasystem ,asarenderingdrivensoftwareplatform ,hasbeenwidelyusedinsystemsimulationandvirtualreality .ItismainlyusedintheUNIXplatform .BecauseoftheeasyuseandapplicationneedoftheWindowsNT ,thesystemofVegahasalsobeentransplantedtoWindowsNTfrom…  相似文献   

8.
A perturbation-based Fourier series model is proposed to approximate the nonlinear distortion in weakly nonlinear circuits. This general model is applicable to any set of multi-variable state equations that completely describe a nonlinear circuit. This model is applied to a common emitter amplifier circuit wherein the transistor is represented by Ebers–Moll nonlinear current equations. Appropriate state variables are defined, then the linear and nonlinear parts of the Ebers–Moll current equations are separated, and a small perturbation parameter is incorporated into the nonlinear part. Now these current equations are incorporated into the set of KCL, KVL equations defined for the circuit and the state variables are perturbatively expanded. Hence, multi-variable state equations are obtained from these equations. The state variables are approximated up to first order through Fourier series expansion, as described in the proposed model. The main advantage of the proposed model is that it is simple and straightforward approach to analyze weakly nonlinear circuits, as it involves matrix computations and the calculations of exponential Fourier coefficients.  相似文献   

9.
We give a careful, fixed-size parameter analysis of a standard (Blum and Micali in SIAM J. Comput. 13(4):850–864, 1984; Goldreich and Levin in Proceedings of 21st ACM Symposium on Theory of Computing, pp. 25–32, 1989) way to form a pseudo-random generator from a one-way function and then pseudo-random functions from said generator (Goldreich et al. in J. Assoc. Comput. Mach. 33(4):792–807, 1986) While the analysis is done in the model of exact security, we improve known bounds also asymptotically when many bits are output each round and we find all auxiliary parameters efficiently, giving a uniform result. These optimizations makes the analysis effective even for security parameters/key-sizes supported by typical block ciphers and hash functions. This enables us to construct very practical pseudo-random generators with strong properties based on plausible assumptions.  相似文献   

10.
An authenticated encryption scheme is a symmetric encryption scheme whose goal is to provide both privacy and integrity. We consider two possible notions of authenticity for such schemes, namely integrity of plaintexts and integrity of ciphertexts, and relate them, when coupled with IND-CPA (indistinguishability under chosen-plaintext attack), to the standard notions of privacy IND-CCA and NM-CPA (indistinguishability under chosen-ciphertext attack and nonmalleability under chosen-plaintext attack) by presenting implications and separations between all notions considered. We then analyze the security of authenticated encryption schemes designed by “generic composition,” meaning making black-box use of a given symmetric encryption scheme and a given MAC. Three composition methods are considered, namely Encrypt-and-MAC, MAC-then-encrypt, and Encrypt-then-MAC. For each of these and for each notion of security, we indicate whether or not the resulting scheme meets the notion in question assuming that the given symmetric encryption scheme is secure against chosen-plaintext attack and the given MAC is unforgeable under chosen-message attack. We provide proofs for the cases where the answer is “yes” and counter-examples for the cases where the answer is “no.” M. Bellare’s work was supported in part by a 1996 Packard Foundation Fellowship in Science and Engineering, NSF CAREER Award CCR-9624439, NSF grants CNS-0524765 and CNS-0627779, and a gift from Intel Corporation. C. Namprempre’s work was supported in part by grants of the first author and the Thailand Research Fund.  相似文献   

11.
As for single mode symmetric step refractive index structure dielectric planar optical waveguide, when its output end is restricted, the diffractive field distribution is derived. It can be expressed as the convolution between the Dirac function and the Sinc and Lorenz functions. It is helpful to deepen the recognition of the restricted diffraction. The characteristic of the diffractive field is discussed. The variational curve of the full angle width at half maximum intensity of central bright fringe versus the half width of slit is presented by numerical calculation, and the fitting curve with the exponential function is close to it.  相似文献   

12.
AnalysisoftheSpherical-CircularPatchAntenna¥LiaoChengenandLiuQing(Xi'anInstituteofPostsandTelecommunications,Xi'an,710061,P.R...  相似文献   

13.
Powerconnector,asonekindoffittings,isusedtoconnectpowerequipmenttoconductor,con ductortowireorwiretowireinpowerlines.Owingtoitssimplestructure ,easyinstallationandlowcost,bolt type powerconnector parallel grooveclampiswidelyusedinoverheadpowertransmissiona…  相似文献   

14.
1 IntroductionRecentlyOFDMtechniquehasregainedlotsofinterestforitspromisingtosupportbroadbandwire lessaccesssystems[1~ 4] .Comparedwithsingle car riersystems,OFDMsystemshavemanyobviousad vantages,suchasrobustnessagainstmultipathdelayspread,feasibilityinhardwareimplementation ,flexibilityinsubcarrierallocationandadaptabilityinsubcarriermodulation[5~6] .However,thepriorityofOFDMsystemscomesfromtheorthogonaldivi sionofbandwidth .Themoredivision ,thelongerthesymbolperiodisandthemorerobustt…  相似文献   

15.
At CRYPTO ’94, Tillich and Zémor proposed a family of hash functions, based on computing a suitable matrix product in groups of the form SL2(\mathbbF2n)SL_{2}(\mathbb{F}_{2^{n}}). We show how to construct collisions between palindromic bit strings of length 2n+2 for Tillich and Zémor’s construction. The approach also yields collisions for related proposals by Petit et al. from ICECS ’08 and CT-RSA ’09.  相似文献   

16.
TheAnalysisofthePostalIndividualFinanceManuscriptreceivedFeb.7,1996LangQiuhong(ShijiazhuangPostalColege,Shijiazhuang050021,P....  相似文献   

17.
We present an efficient framework for dynamic reconfiguration of application-specific custom instructions. A key component of this framework is an iterative algorithm for temporal and spatial partitioning of the loop kernels. Our algorithm maximizes the performance gain of an application while taking into consideration the dynamic reconfiguration cost. It selects the appropriate custom instructions for the loops and clubs them into one or more configurations. We model the temporal partitioning problem as a k-way graph partitioning problem. A dynamic programming based solution is used for the spatial partitioning. Comprehensive experimental results indicate that our iterative partitioning algorithm is highly scalable while producing optimal or near-optimal (99% of the optimal) performance gain.  相似文献   

18.
19.
TheCapacityAnalysisoftheCDMACellularSystem¥ZhangPing(DepartmentofTelecommunicationEngineering,BeijingUniversityofPostsandTele...  相似文献   

20.
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