共查询到20条相似文献,搜索用时 31 毫秒
1.
本工作以疏波短声作为刺激声在35位受试者(58耳)分别测出诱发性耳声发射(EOAE)、行为反应(BR)及听觉脑干反应(ABR)的阈值.闭值的主要分布范围:EOAE为10-45dB(nHL),占总数的86%;为10-25dB,占88%;ABR为10-35dB,亦占88%.所有受试耳的三种阈值的相关系数 r:EOAE-BR为0.415( p<0.002).EOAE-ABR为0.501( p<0.001),ABR-BR为0.702( p<0.001),均呈显著相关.若仅取BR、ABR或EOAE阈值≥25dB的耳作统计,则EOAE-BR间的 r只有0.176及0.292;EOAE-ABR的 r只有0.310及0.300,无相关( p0.05),而ABR-BR间的 r仍有0.533及0.720,( p<0.05),这些结果表明EOAE与听阈之间只有在后者正常或稍升高时才有一定的相关,当听阈上升较多时相关即不存在.EOAE可以作为听力学检查的一种辅助方法,但不能用它推算听阈. 相似文献
2.
The purpose of this investigation was to correlate magnetic resonance (MR) perfusion measurements with absolute regional cerebral blood flow (rCBF) in a rat model of focal ischemia. The MR perfusion measurements were made using dynamic first-pass bolus tracking of a susceptibility contrast agent, whereas rCBF was measured using radioactive microspheres. Two simple MR perfusion parameters, the maximum change in
(
) and time delay to
(
), were derived from the signal intensity versus time curves on a pixel-to-pixel basis, without applying curve-fitting procedures or tracer kinetic theory. In each hemisphere,
and
were compared with the rCBF measurements in four selected regions of interest. Sixteen MR bolus tracking series were performed in 12 rats with occlusion of the middle cerebral artery. In all of the individual series there was a significant correlation (.0001 ≤ p ≤ .02) between
and the microsphere rCBF measurements, with correlation coefficients ranging from .784 to .983. Pooling the
data resulted in a correlation coefficient of .809 ( p = .0001). There was a nonlinear correlation between the
and rCBF. For both parameters there was considerable variation between different measurements regarding both the slope of the regression line and its intercept with the y-axis. Our results justify the use of
as a relative measure of perfusion during acute cerebral ischemia. Because of the interindividual variation, calibration of MR perfusion measurements for the estimation of absolute flow values must be considered unreliable. The
may have physiological relevance as a marker of collateral flow. 相似文献
3.
以平衡点参数 p, q构造出一类对称三稳势函数, 进而提出微弱信号和噪声共同驱动的三稳系统模型. 深入研究并总结参数 p, q对势垒高度Δ U1, Δ U2及两势垒高度差的影响. 从定常输入的角度提出了系统稳态解曲线的概念, 并进一步研究低频谐波信号输入时系统的输出动态响应. 引入噪声, 三稳系统在合适的参数条件下实现随机共振, 从稳态解曲线的角度分析了噪声诱导的三稳系统随机共振机理. 最后研究了阻尼比 k和平衡点参数 p, q对系统随机共振的影响. 相似文献
4.
构造了一种特殊的阵列结构,定义了子阵列输出信号之间的互协变异矩阵,提出了一种在 SαS噪声环境中基于分数低阶矩的二维子空间测向算法。该算法利用 SαS过程具有 p( p≥ α)阶矩无限、而分数 p(0≤ p< α)阶矩有限等特点,扩展了二维测向算法的信号模型和应用环境,对加性 SαS噪声有较好的抑制作用,弥补了传统的基于二阶和高阶统计量的子空间测向算法不能应用于冲击噪声环境的不足。计算机仿真验证了该算法的可行性和有效性。 相似文献
5.
The construction of wavelets begins with a dilation equation ( x) = Σ ck(2 x- k). The choice of the coefficients ck controls the accuracy and orthogonality of wavelet expansions. We show how the Daubechies coefficients, which give pth order accuracy with 2 p coefficients (the minimum number), follow from orthogonality and accuracy conditions applied to the polynomial Σ cke ikξ. 相似文献
6.
The transition from phase chaos to defect chaos in the complex Ginzburg–Landau equation (CGLE) is related to saddle-node bifurcations of modulated amplitude waves (MAWs). First, the spatial period P of MAWs is shown to be limited by a maximum PSN which depends on the CGLE coefficients; MAW-like structures with period larger than PSN evolve to defects. Second, slowly evolving near-MAWs with average phase gradients ν≈0 and various periods occur naturally in phase chaotic states of the CGLE. As a measure for these periods, we study the distributions of spacings p between neighbouring peaks of the phase gradient. A systematic comparison of p and PSN as a function of coefficients of the CGLE shows that defects are generated at locations where p becomes larger than PSN. In other words, MAWs with period PSN represent “critical nuclei” for the formation of defects in phase chaos and may trigger the transition to defect chaos. Since rare events where p becomes sufficiently large to lead to defect formation may only occur after a long transient, the coefficients where the transition to defect chaos seems to occur depend on system size and integration time. We conjecture that in the regime where the maximum period PSN has diverged, phase chaos persists in the thermodynamic limit. 相似文献
7.
In this paper some results are presented concerning one-dimensional chaotic maps with arbitrarily many critical points. Let f be a chaotic map belonging to some suitable class of C 1 maps from a nontrivial interval X into itself. Assuming that f is of class C1+ for some > 0, we have that the set of aperiodic points for f has Lebesgue measure zero; further, if f(X) is bounded then there exists a positive integer p such that almost every point in the interval is asymptotically periodic with period p. Moreover, it will turn out that this asymptotically periodic behaviour in the complicated dynamics of f is persistent under small smooth perturbations. The topological structure of the nonwandering set of f will be described, and this structure is invariant under small C1 perturbations of the map f. Assuming that f is of class C2, the map f is C2 structurally stable provided that f satisfies some suitable conditions. Finally, it will turn out that maps with a negative Schwarzian derivative belong to the suitable class of maps mentioned above. 相似文献
8.
An iterated function system (IFS) over a compact metric space X is defined by a set of contractive maps wi: X → X, i = 1,…, N, with associated nonzero probabilities pi > 0, pi = 1. The “parallel” action of the maps defines a unique compact invariant attractor set A X which supports an invariant measure μ and which is balanced with respect to the pi. For linear
, the invariance of μ yields a relation between the moments gn = ∫ χ n dμ which permits their recursive computation from the initial value g0 = 1. For nonlinear wi, however, the moment relations are incomplete and do not permit a recursive computation. This paper describes two methods of obtaining accurate estimates of the moments when the IFS maps wi are polynomials: (i) application of the necessary Hausdorff conditions on the gi to obtain convergent upper and lower bounds and (ii) a perturbation expansion approach. The methods are applied to some model problems. 相似文献
9.
The “vehicular effects” of chain segment motion on ionic diffusion in solid polymer electrolytes have been investigated via numerical simulation on a two-dimensional square lattice where the dynamical variation of chain configuration is presented by translational or rotational bond movement. It is found that (a) both types of bond motion promote continuous diffusion when the fraction ( p) of available bonds is below the static percolation threshold of p=0.5 in two dimensions; (b) translational motion of bonds parallel to the direction of diffusion produces larger diffusion coefficients ( D) than that by random renewal of the dynamic bond percolation model (DBPM), while the perpendicular motion or rotational motion gives smaller values of D; (c) Smooth lines instead of “stair-case like” curves generated by DBPM are obtained in the mean-squared displacement versus time plot, when bonds are shifting along the diffusion route. The dependence of diffusion coefficients on the variation of motion patterns of bonds is expected to be related to the temperature change under which these patterns are excited accordingly, such that VTF behavior of certain polymer electrolytes may be deduced. 相似文献
10.
Following Kostov and Ben-Menahem, we calculate the two-puncture correlation function for the one-dimensional matrix model. We find that it depends on the details of discretization for all momenta p. Its only universal features are its vanishing as p → 0 and the appearance of double poles at | p| = n/√′, N = 1,2,…. We show how to derive these double poles in the conformal gauge treatment of Liouville gravity. 相似文献
11.
This study was designed to evaluate a disease-specific outcome measure for patients with selected voice disorders and to relate this instrument to a standardized quality of life measurement. In addition, the study attempts to document the degree of handicap for dysphonia patients globally, between different vocal pathologies, and in comparison to other chronic diseases. In this prospective, observational study, 260 adult patients evaluated for alterations of voice completed a general quality of life measure (the Medical Outcomes Trust Short Form 36-Item[SF-36]) and a voice-specific instrument (Voice Handicap Index [VHI]) pretreatment. The highest correlation was between the social functioning score of the SF-36and the total score of the VHI and the physical, emotional, and functional subscales (p < 0.001) of the VHI. Significant correlation was also obtained for the SF-36 domains mental health (p < 0.01), general health (p < 0.01), and role functioning emotional (p < 0.017) with the three VHI domains and the total VHI score. Patients had significantly lower scores than the general U.S. population in five of the eight domains of SF-36. Patients with vocal fold paralysis had the highest level of pretreatment disability as measured on both the VHI and SF-36 among voice patients. The patients with dysphonia had a lower level of physical functioning than the patients with chronic sinusitis (p < 0.01), reflecting a greater handicap. In addition, the dysphonia group had lower levels of social functioning than the angina (p < 0.01) and sciatica (p < 0.01) groups and a lower score for mental health than the angina group (p < 0.01). The SF-36 correlates with the VHI in the domains of social functioning,mental health, and role functioning emotional. The baseline handicap for voice disorders represents a significant disability even in comparison to conditions such as angina pectoris, sciatica, and chronic sinusitis. 相似文献
12.
The reaction e + p → e + π 0 + p was measured near the one pion threshold, detecting the final electron and proton in coincidence for values of q2 = 0.2, 0.4 and 0.6 GeV 2. The slope of the cross section at threshold is determined. The data are compared with those of the e + p → e + π + + n reaction, measured simultaneously, and with the results of pseudovector Born approximation and with dispersion theoretical calculations. 相似文献
13.
The pressure effect on Tc of polycrystalline and single crystalline YBa 2Cu 3O x investigated as a function of oxygen content x by ac-susceptibility measurements under helium pressure. In the overdoped region x> 6.93 the single crystals show a negative d Tc/d p, as expected from the charge transfer model. For optimally doped samples with x = 6.93 we find d Tc/d P = 0.4 K/GPa which points to pressure effects on Tc aside from charge transfer. In the underdoped region x < 6.93 the d Tc/d p values obtained from the experiment depend strongly on the storage temperature of the sample during the experiment. When the samples are stored at temperatures well below 240 K throughout the entire experiment including pressure application and pressure release, d Tc/d p increases to approx. 7 K/GPa at x = 6.7 but with a further decrease of the oxygen content the d Tc/d p drops to approx. 2 K/GPa at x = 6.4. These effects are intrinsic to the YBa 2Cu 3O x structure and can be explained by considering the anisotropic structure of YBa 2Cu 3O x. The decrease of the c-axis lattice parameter results in a charge transfer to the CuO 2-planes mainly [1], whereas the compression of the a- and b-axis lattice parameter is known to produce different pressure effects which are responsible for the peak in d Tc/d p at x = 6.7 [2]. When pressure is changed at room temperature oxygen ordering effects occur which cause a relaxation of Tc to the equilibrium value Tc( p) at this pressure with a time constant depending on the oxygen content x. A decrease x results in a peak effect in d Tc/d p at x = 6.7 again, which is enhanced to approx. 12 K/GPa. If the oxygen content is decreased further, d Tc/d p first drops to 5 K/GPa at x = 6.6, but the increases to values of more than 20 K/GPa for x < 6.42. These giant pressure effects at low oxygen contents are mainly caused by a reversible Tc increase (d Tc/d p) O due to pressure induced oxygen ordering via oxygen motion between unit cells. 相似文献
14.
Photoemission measurements of Rh films in the photon energy range 40–120 eV show that the 4 p-4 d intrashell interaction has a Fano-like resonance. The 4 d photoemission intensity goes through a sharp dip in the vicinity of the 4 p64 dn+ hv → 4 p54 dn+1 threshold followed by a resonant enhancement before decreasing again. All parts of the 4 d band show the same resonant behavior in contrast to previous resonant photoemission results. The resonant behavior of Rh is compared with Co which is the 3 d analog of Rh. 相似文献
15.
To search for new candidates of the true and simultaneous two-proton(2 p) radioactivity, the 2 p decay energies(Q2 p) are extracted by the Weizs?cker–Skyrme-4(WS4) model, the finite-range droplet model(FRDM), the Koura–Tachibana–Uno–Yamada(KTUY) model and the Hartree–Fock–Bogoliubov mean-field model with the BSk29 Skyrme interaction(HFB29). Then, the 2 p radioactivity half-lives are calculated within the generalized liquid drop model by inputting the four types of Q2 pvalues. By the energy and half-life constraints, it is found that the probable 2 p decay candidates are the nuclei beyond the proton-drip line in the region of Z≤50 based on the WS4 and KTUY mass models. For the FRDM mass model, the probable 2 p decay candidates are found in the region of Z≤44. However, the 2p-decaying candidates are predicted in the region of Z≤58 by the HFB29 mass model. It means that the probable 2 p decay candidates of Z50 are only predicted by the HFB29 mass model. Finally, the competition between the true 2p radioactivity and α-decay for the nuclei above the N=Z=50 shell closures is discussed. It is shown that ~(101)Te,~(111)Ba and ~(114)Ce prefer to 2p radioactivity and the dominant decay mode of ~(107)Xe and ~(116)Ce is α-decay. 相似文献
16.
当 k的值不大时(例如 k≤4),诸系数 γiγi*, βkρ, βkρ*易于手工计算。但对大的 k值(例如 k≥5),手工计算已非易事。利用著名的计算机代数软件:REDUCE [a],我们可以很容易地计算出诸系数 γi, γi*, βkρ, βkρ*。 相似文献
17.
The present paper studies ductile fracture by a random fractal and calculates the fracture probability q of a ductile fracture. The fracture probability q is sensitive to the number n (microvoid size) and the probability p of forming microvoids. There are two critical probabilities pc1 and pc2. When ppc2 = 1-1/ n2, the fracture probability q is 100%, the ductile fracture occurs with probability 1; when pc2 > p> pc1, there is a positive probability q (1> q>0), the fracture probability q increases with increasing probability p and/or decreasing number n; when p< pc1, the fracture probability q is zero (in fact less than 0.00001), the fracture does not occur. The critical probabilities pc1 and pc2 increase with increasing n. When 1-1/ n2> p>1-1/ n, though a ductile fracture does not occur, there is at least a macrovoid which passes through the transverse plane of the specimen. 相似文献
18.
The dimensionally regularized massless non-planar double box Feynman diagram with powers of propagators equal to one, one leg off the mass shell, i.e., with p12= q2≠0, and three legs on shell, pi2=0, i=2,3,4, is analytically calculated for general values of q2 and the Mandelstam variables s, t and u (not necessarily restricted by the physical condition s+ t+ u= q2). An explicit result is expressed through (generalized) polylogarithms, up to the fourth order, dependent on rational combinations of q2, s, t and u, and simple finite two- and three-fold Mellin–Barnes integrals of products of gamma functions which are easily numerically evaluated for arbitrary non-zero values of the arguments. 相似文献
19.
While BOLD contrast reflects hemodynamic changes within capillaries serving neural tissue, it also has a venous component. Studies that have determined the relation of large blood vessels to the activation map indicate that veins are the source of the largest response, and the most delayed in time. It would be informative if the location of these large veins could be extracted from the properties of the functional responses, since vessels are not visible in BOLD contrast images. The present study describes a method for investigating whether measures taken from the functional response can reliably predict vein location, or at least be useful in down-weighting the venous contribution to the activation response, and illustrates this method using data from one subject. We combined fMRI at 3 Tesla with high-resolution anatomic imaging and MR venography to test whether the intrinsic properties of activation time courses corresponded to tissue type. Measures were taken from a gamma fit to the functional response. Mean magnitude showed a significant effect of tissue type ( p < 0.001) where CSF > veins ≈ gray matter > white matter. Mean delays displayed the same ranking across tissue types ( p < 0.001), except that veins > gray matter. However, measures for all tissue types were distributed across an overlapping range. A logistic regression model correctly discriminated 72% of the veins from gray matter in the absence of independent information of macroscopic vessels (ROC = 0.72). While tissue classification was not perfect for this subject, weighting the T contrast by the predicted probabilities materially reduced the venous component to the activation map. 相似文献
20.
We have used electron spin resonance measurements to derive the temperature and frequency dependences of the field-induced magnetization [ M( T, f)] and anisotropy field [ Han ( T)] in a number of amorphous alloys belonging to the series (Fe pNi 1−p) 75P 16B 6Al 3. In re-entrant ( p > pc, the critical concentration for ferromagnetism) alloys at hi gh frequencies ( f = 35 GHz, field ≈ 12 kOe) M reduces as T3/2 at high T and as T below ≈ 40 K, the deviation from T3/2 becoming more marked as p → p+c. For p close to pc, lowering the frequency first causes the T
term to increase and ultimately ( ≈ 4 GHz) changes the variation of M with T to that discovered previously for concentrated spin glasses, namely M is constant at low T and drops linearly at high temperatures. For the re-entrants, the results are interpreted on the basis of a model which invokes an energy gap in the spin-wave spectrum, introduces a non-zero density of states of the gap energy and takes into consideration a low- q cut-off in the spin-wave integral in thelow- T ( T) regime.In the concentrated spin glasses [ M (0) - M ( T)]/ M (0) is well represented by the function [exp (Δ / T) - 1] -1, where Δ has values close to the corresponding Curie-Weiss temperatures θ p but much larger than the respective spin glass transition temperatures TSG. The temperature dependence of Han is largely given by the function (1 - T/ T*), where T* is equal to the zero-field freezing temperature for the re-entrants and TSG for the spin glasses, respectively. 相似文献
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