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1.
初中物理:“水的热膨胀的特点”的演示在我数年的教学中一直没有做过,这主要是因为:当堂演示太费时间又和讲课配合不好,如让学生等着看实验结果,则大部同学感到索然无味,如不等结果而先讲其他内容,则又打乱了课堂的系统性。加以有些学校根本没有水的最大密度演示器,因之过去讲这一节时,往往只用挂图一讲了事。但后来在物理通报上看到一些老师对这个演示采取了各种不同的方法,从而取得了较好的成绩。为了提高教学质量,我把通报上前后所介绍的几种方法都做了几遍,从不断变换着的操作中给了我新的启示,我又用了 相似文献
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初中物理学上册第三章第35节大气压的一个实验是:水由喷嘴向压强较低的玻璃管中喷入(见原书图55)。这个实验如果没有抽气机,就很难做。我 相似文献
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O. V. Bocharova M. G. Lebedev 《Russian Journal of Physical Chemistry B, Focus on Physics》2011,5(4):589-596
The self-oscillatory interaction of supersonic jets with barriers has mainly been studied for under-expanded jets. There are
only a few experimental studies examining the case of overexpanded jets, with little computational work done in this direction.
To fill this gap, we performed numerical simulations of overexpanded supersonic jets with barriers. The calculations were
performed by the Godunov method on fine grids using parallel programming techniques. In the course of numerical simulations,
the gasdynamic parameters of the jet and the geometric parameter of the barrier were varied. The barrier had the shape of
a cylindrical cavity of depth l = (0 − 18)r
a
, where r
a
is the nozzle exit radius (the case l = 0 corresponds to a flat-end barrier). Based on the results of the numerical simulations, the conclusion on whether the
self-oscillation process occurs was drawn and the dependence its characteristics (frequency and amplitude) on the governing
gasdynamic and geometric parameters were obtained. Good agreement with experimental data on the fundamental tone frequency
was demonstrated. A low-frequency oscillation mode was mostly realized. In this case, the jet experienced periodic suctions
into and ejections from the cavity, counter the oncoming jet flow, with the formation of a structure consisting of three discontinuity
surfaces (two shock waves and a separating surface contact). 相似文献
12.
A boundS
l is given for the number of bound statesn
i in thelth partial wave corresponding to a spherically symmetric potential in non-relativistic quantum mechanics. This bound is given
by
whereV
a(l, r) is the attractive part of the effective potentialV(r)+l(l+1)/r
2. Extensive comparative study ofS
i and the Bargmann inequality is made. 相似文献
13.
A linear correlation between the Grüneisen parameter and ratio of the velocities of longitudinal (ν
l)and transverse (ν
t) acoustic waves in crystals is found. It is assumed that velocities ν
l and ν
t are severally harmonic parameters, while their ratio ν
l/ν
t is an anharmonic quantity and depends on the ratio between the shear and flexural rigidities of interatomic bonds. 相似文献
14.
B. Schommartz D. Ziegler P. Schadewaldt 《Isotopes in environmental and health studies》2013,49(1-2):135-143
Abstract Two novel characteristic parameters, the latency time (t lat) and the ascension time (t asc), are proposed for evaluation of non-invasive [13C]octanoic acid breath tests for assessment of the gastric emptying of solids. In breath tests performed in control subjects (n = 30) and diabetic patients (n = 100), the usefulness of these parameters was compared to conventional parameters, i.e., gastric half emptying-time t 1/2,b ) and lag phase (t lag,b ). The proposed parameters were only loosely correlated (controls, r = 0.199; diabetics, 0.616). A strong correlation was found between the conventional parameters (controls, r = 0.891; diabetics, r = 0.962). Based on the conventional method, 36 patients were suspicious of delayed gastric emptying including 24 patients which exhibited a simultaneous delay in both parameters. Using the new parameters, a total of 46 patients were suspicious of delayed gastric emptying with 15 and 20 having isolated delay in t lat and t asc, respectively. We conclude that the novel parameters may be more appropriate for examination of the different phases of gastric emptying and for evaluation of gastric emptying disturbances in diabetic patients than the parameters conventionally used for this purpose. 相似文献
15.
R. P. Babertsyan É. S. Badalyan G. A. Égiazaryan É. I. Ter-Gevorkyan V. N. Ogannisyan 《Technical Physics》2000,45(4):406-410
The mechanisms of processes determining distribution of positive ions on the cathode surface in a discharge with oscillating electrons are studied. At low pressures P≤5×10−5 torr over the entire range of anode length variation l a=0.5–11 cm, the ion current distribution over the cathode radius J i(r) features a single maximum in the center and drops steeply with distance from the axis. At pressures P=1–4×10−4 torr, the distribution J i(r) for short anodes (l a<6 cm) is similar to the previous one but, for long anodes (l a=6–10 cm), new maxima at higher J i values have been detected. A physical explanation for the obtained results is proposed. 相似文献
16.
Using intensity autocorrelation of multiply scattered light, we show that the increase in interparticle interaction in dense,
binary colloidal fluid mixtures of particle diameters 0.115μm and 0.089μm results in freezing into a crystalline phase at volume fractionφ of 0.1 and into a glassy state atφ=0.2. The functional form of the field autocorrelation functiong
(1)(t) for the binary fluid phase is fitted to exp[−γ(6k
0
2
D
eff
t)1/2] wherek
0 is the magnitude of the incident light wavevector andγ is a parameter inversely proportional to the photon transport mean free pathl*. TheD
eff is thel* weighted average of the individual diffusion coefficients of the pure species. Thel* used in calculatingD
eff was computed using the Mie theory. In the solid (crystal or glass) phase, theg
(1)(t) is fitted (only with a moderate success) to exp[−γ(6k
0
2
W(t))1/2] where the mean-squared displacementW(t) is evaluated for a harmonically bound overdamped Brownian oscillator. It is found that the fitted parameterγ for both the binary and monodisperse suspensions decreases significantly with the increase of interparticle interactions.
This has been justified by showing that the calculated values ofl* in a monodisperse suspension using Mie theory increase very significantly with the interactions incorporated inl* via the static structure factor. 相似文献
17.
J. Dušek 《Czechoslovak Journal of Physics》1982,32(12):1325-1348
On the basis of the Gell-Mann — Goldberger two-potential formalism we investigate the partial waves of an off-shell two-body T-matrix in the case of a general Coulomb-like potentialV=V
C
+V
S
. The regular kernelt
SC,l
determining thel-th partial wave of the short-range partT
SC,l
of the T-matrix is the solution of the equationt
SC,l
=V
S,l
+V
S,l
G
C,l
t
SC,l
. The Lippmann-Schwinger operator of this equation formed by the short-range part of the potential and the pure Coulomb Green's operator is shown to be compact under very general assumptions on the potentialV
S
admitting potentials vanishing in the coordinate representation liker
–1–
(>0) in the infinity. The special case of differentiable and analytic potentialsV
S,l
(p,p) is considered in particular. The results are used to discuss in full generality the on-shell singularities of Coulomb-like T-matrices and wave functions and to investigate the singular integrals that occur in the Faddeev equations for Coulomb-like interactions. 相似文献
18.
R. P. Babertsyan É. S. Badalyan G. A. Egiazaryan É. I. Ter-Gevorkyan 《Technical Physics》1998,43(9):1035-1038
A steady-state Penning ion source is studied experimentally. Depending on the geometric parameter l
a
(the anode length to diameter ratio) and pressure, maxima are observed in the discharge current and in the ion beam current
extracted from an aperture at the center of the cathode. It is shown that at pressures of the order of 10−4 Torr, two maxima appear in these currents: one, for short discharge gaps with l
a
=1–1.5, corresponds to a diverging ion beam, and the other, for longer anodes with l
a
=4–5, to a collimated ion beam. At pressures of the order of 10−5 Torr, only one maximum appears in these currents, for short anodes l
a
=2–3 with a diverging ion beam. A physical explanation is proposed for these findings.
Zh. Tekh. Fiz. 68, 29–32 (September 1998) 相似文献
19.
A geometric construction of a certain singular unitary representation ofSO
e(p,q), withp+q even is given. The representation is realized geometrically as the kernel of aSO
e(p,q)-invariant operator on a space of sections over a homogeneous space forSO
e(p,q). TheK-structure of these representations is elucidated and we demonstrate their unitarity by explicitly writing down anso(p,q) positive definite hermitian form. Finally, we demonstrate that the annihilator inU[g] of this representation is the Joseph ideal, which is the maximal primitive ideal associated with the minimal coadjoint orbit. 相似文献
20.
L. I. Korovin I. G. Lang D. A. Contreras-Solorio S. T. Pavlov 《Physics of the Solid State》2000,42(12):2300-2313
A theory for the response of a 2D two-level system to irradiation by a symmetric light pulse is developed. Under certain conditions, such an electron system approximates an ideal solitary quantum well in a zero field or a strong magnetic field H perpendicular to the plane of the well. One of the energy levels is the ground state of the system, while the other is a discrete excited state with energy ?ω0, which may be an exciton level for H=0 or any level in a strong magnetic field. It is assumed that the effect of other energy levels and the interaction of light with the lattice can be ignored. General formulas are derived for the time dependence of the dimensionless “coefficients” of the reflection ?(t), absorption A(t), and transmission ?(t) for a symmetric light pulse. It is shown that the ?(t), A(t), and ?(t) time dependences have singular points of three types. At points t 0 of the first type, A(t 0)=T(t 0)=0 and total reflection takes place. It is shown that for γr?γ, where γr and γ are the radiative and nonradiative reciprocal lifetimes, respectively, for the upper energy level of the two-level system, the amplitude and shape of the transmitted pulse can change significantly under the resonance ωl=ω0. In the case of a long pulse, when γl<γr, the pulse is reflected almost completely. (The quantity γl characterizes the duration of the exciting pulse.) In the case of an intermediate pulse duration γl?γr, the reflection, absorption, and transmission are comparable in value and the shape of the transmitted pulse differs considerably from the shape of the exciting pulse: the transmitted pulse has two peaks due to the existence of the point t 0 of total reflection, at which the transmission is zero. If the carrier frequency ωl of light differs from the resonance frequency ω0, the oscillating ?(t), A(t), and ?(t) time dependences are observed at the frequency Δω=ωl?ω0. Oscillations can be observed most conveniently for Δω?γl. The position of the singular points of total absorption, reflection, and transparency is studied for the case when ωl differs from the resonance frequency. 相似文献