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1.
Summary We present here measurements of hyperfine splittings andg factors of two nitroxide spin probes dissolved inp-azoxyanisole, a wellknown uniaxial nematic liquid crystal, about one part to a million in their molecular ratio. The spin
probe molecules used are 1) 17β-hydroxy-4′, 4′-dimethylspiro-/5α-androstane-3, 2′-oxazolidin/-3′-yloxyl, and 2) 2-(3-Carboxypropyl)-4,
4-dimethyl-2-tridecyl-3-oxazolidinyloxyl methyl ester; the former is known to have rigid and the latter flexible structures.
These results are used to demonstrate the validity of our model that relates the orientational-order tensor
of liquid crystals to the above quantities obtained by the electron spin resonance technique. The model is free of restrictions
on the nature of the solute molecules, rigid or flexible. The relation between these directly measured quantities and the
components of
is established in two steps: first by relating them to
, an order parameter tensor defined by a unit vector along the so-called long axis of solute molecules, and then by the use
of
, wherek is a scalar constant. This latter relation is obtained on the plausible arguments of solute-solvent and solvent-solvent interactions
giving rise to
and
, respectively, andk representing their relative strengths. In spite of appreciable structural differences existing between these two solute molecules,
very satisfactory agreements between the theory and experiment are observed for both. Such agreements are essentially independent
of uncertainties in our knowledge of the parameters involved. Furthermore, we show that important molecular parameters can
also be obtained from such measurements.
Deceased. 相似文献
2.
Summary Frequency distributions of energy deposition in microscopic tissue volumes determined by means of a ?Rossi type? proportional
counter for 31, 12 and 8 MeV proton beams and, dose response curves for mortality and chromosome aberrations in cultured human
cells exposed to the same beams are analysed with a view to determining suitable parameters to specify radiation quality.
The behaviour of quantities LET,Z
*2/β2 and the microdosimetric parameter
as a function of energy are compared with the corresponding behaviour of the most significant radiobiological parameters
as mean lethal dose per targetD
0, mean inactivation dose
, intensity of chromosome aberrations, and dicentrics. It is shown that
is the most suitable physical parameter to characterize the relative effectiveness of protons in the (8÷31) MeV range.
Work partially supported by grant No. 8000165896 for the Finalized Project ?Tumor Growth Control?. 相似文献
3.
4.
The maximum number of non-vanishing and independent second order photoelastic coefficients required by the seven pentagonal
and the two icosahedral point groups 5(C5),
(S10),
(C5h
),
m2(D5h
), 52(D5), 5m(C5v
),
2m(D5d
); 235(I), 2/m
(I
h
)—that describe the quasicrystals symmetry groups in two and three dimensions—is obtained. The schemes of non-vanishing and
independent coefficients have been calculated and listed. Finally the results of this group-theoretical study are briefly
discussed. 相似文献
5.
Summary Grain growth is studied in polycrystalline ice, consisting of elongated grains, of (200÷300) μm mean width
and (2÷3) mm mean length
. The samples are annealed at different temperatures, between 0°C and −10°C. It is found that
is not affected by annealing, while
increases with the annealing time. Below the melting point,
(t) tends to a limit value
. This behaviour is related to the pinning action of air bubbles, which would be similar to that found for solid inclusions
in metals. By assuming
where
is the mean bubble diameter andf is the volume fraction of air dissolved in water, reasonable values are found for
. The activation energy of the phenomenon is evaluated on the basis of the present and of Jellinek and Gouda's results. It
is foundQ=0.6 eV, which value approximately coincides with that for bulk self-diffusion as it occurs for metals, several degrees below
the melting point. This coincidence suggests that, for ice, grain growth would be controlled by bulk impurity diffusion up
to the very melting point.
Instituto de Matemática, Astronomía y Física, Universidad Nacional de Córdoba and CONICET. 相似文献
6.
Gely F. Zharkov 《Central European Journal of Physics》2005,3(1):77-103
Self-consistent solutions of the nonlinear Ginzburg-Landau (GL) equations are investigated numerically for a superconducting
(SC) cylinder, placed in an axial magnetic field, with a single vortex on the axis (m=1). Two modes, which show the original state of the cylinder, SC or normal (s
0 andn
0), are studied. The field increase (FI) and the field decrease (FD) regimes are studied. The critical fields destroying the
SC state withm=1 are found in both regimes. It is shown that in a cylinder of radiusR and GL-parameter ϰ, there exist a number of solutions depending only on the radial co-ordinater corresponding to different states such as M,e, d, p,i, n,
,n
*, and the state diagram on the plane of the variables (ϰ,R) is described. The critical fields corresponding to intrastate transitions and the onset of hysteresis are obtained. The
critical fieldH
0(R) dividing the paramagnetic and diamagnetic states of the cylinder withm=1 is determined. The limiting fields of supercooling or superheating of the normal state at which the restoration of the
SC state occurs are established. It is shown, that (in both casesm=1,0) there exist two critical parameters,
and
, which divide bulk SC into three groups (with
and
), in accordance with the behavior in a magnetic field. The parameters
and
mark the boundary for the existence of a supercooled normal
-state in FD-regime and a superheated SC M-state in FI-regime respectively. It is shown, that the value
, which was claimed in a number of papers as related to type-I superconductors, is illusory.
We regret to inform that Professor Gely Zharkov passed away on 9th July 2004. 相似文献
7.
Finitely generated free modular ortholattices. II 总被引:2,自引:0,他引:2
M. Haviar P. Konôpka C. B. Wegener 《International Journal of Theoretical Physics》1997,36(12):2661-2679
8.
R. Orbach 《Hyperfine Interactions》1989,49(1-4):325-333
The excitation dynamics of site diluted magnets can be described at low energies (long length scales) by magnons, and above
a crossover frequency, ωc, (short length scales) by fractons. The density of fracton states is given by
, where
is the fracton dimensionality. Dilution gives rise to a characteristic length ξ∝(p−p
c)ν, wherep
c is the critical concentration for (magnetic) percolation. The crossover frequency ωc is proportional to ξ-1[1+(θ/2)], where θ is the rate at which the diffusion constant decays with distance for diffusion on an equivalent network. A fractal
dimensionD describes the density of magnetic sites on the infinite network, and
. For percolating networks,
for all dimensions ≥2. Neutron scattering structure factor measurements by Uemura and Birgeneau compare well with calculations
using fracton concepts.
Magnons are extended at low energies, while the fracton states are geometrically localized, with a wave function envelope
proportional to exp
. Here,
is the fracton length scale at frequency ω. The exponentd
ϕ lies between 1 andd
min, the chemical length index (of the order of 1.6 in three dimensions). The localization of the magnetic excitations causes
a spread in the NMR relaxation rates. A given nuclear moment will experience only a limited set of fracton excitations, resulting
in an overall non-exponential decay of the NMR relaxation signal. When strong cross-relaxation is present, the relaxation
will be exponential, but the temperature dependence will be strongly altered from the concentrated result. 相似文献
9.
10.
We discuss the behavior of magnetically trapped antihydrogen (
) at temperatures relevant for gravity and spectroscopy experiments (well below 1 K) and the possibilities of attaining these
temperatures. Two possible options are considered. In the discussion of the first one, i.e.
as admixture in cold H gas, we develop the quantum-mechanical theory of
-H (and also
-H) elastic and rearrangement collisions at ultra-low (sub-Kelvin) energies, when s-wave scattering in the incoming channel
dominates. The rate constant of rearrangement leading to
decay turns out to be large, which makes the possibilities for
collisional cooling in H gas and
-H coexistence rather limited. As we show, the most promising is the other option, i.e.
atoms in the collisionless regime. For this regime the possibility of one-dimensional adiabatic cooling of
is demonstrated by using the example of the Ioffe trap. This phenomenon, interesting from the fundamental point of view,
offers the opportunity to cool
below 1 mK. 相似文献
11.
The existence of a topological double-covering for the GL(n, R) and diffeomorphism groups is reviewed. These groups do not
have finite-dimensional faithful representations. An explicit construction and the classification of all
(n, R), n=3,4 unitary irreducible representations is presented. Infinite-component spinorial and tensorial
fields, “manifields”, are introduced. Particle content of the ladder manifields, as given by the
(3, R) “little” group, is determined. The manifields are lifted to the corresponding world spinorial and tensorial manifields
by making use of generalized infinite-component frame fields. World manifields transform w.r.t. corresponding
representations, which are constructed explicitly.
Supported in part by the Science Foundation (Belgrade). 相似文献
12.
G. Dietz K. Richter F. Stein H. C. Schäfer 《Zeitschrift für Physik B Condensed Matter》1990,81(2):223-228
Dependent on
is produced through electrodeposition in three modifications: microcrystalline if
, amorphous if
and in a mixed state containing both components if
. The interpretation of results of large and small angle X-ray scattering, of measurements of the coercivity and of the mechanical density shows that the three modifications consist of two phases. The structure of the grain boundary phase in the microcrystalline alloys differs considerably from that of the amorphous phase. This arises from the dependence of the atomic volume on the average phosphorus content
. The volume fraction of the crystalline component decreases with increasing
up to
. But even in alloys revealing X-ray patterns without any peaks coming from crystalline particles small angle X-ray scattering indicates the existence of metal-rich inclusions occupying some percent of the total volume. 相似文献
13.
Garry Ludwig 《General Relativity and Gravitation》1983,15(11):1085-1097
In a recent paper it was shown how to construct, under certain circumstances, asymptotic (Newman-Unti) series expansions for
the spin-coefficient variables for real space-times from data obtained from a given left-flat space in an appropriate frame.
If these expansions represent asymptotically flat space-times the latter have the given left-flat space as their H space.
The method was described in a frame in which the asymptotic left-shear
was zero whereas
was not. For the discussion of algebraically special left-flat spaces it is more convenient to have
vanish and
remain nonzero. In this paper we determine all algebraically special left-flat spaces with diverging rays, utilizing Penrose's
conformal technique, and then show in detail how to find the “initial data” for the construction of asymptotic series expansions
for the corresponding real space-times. 相似文献
14.
Explicit evaluation of the following parameters has been carried out in the extraU (1) superstring inspired model: (i) As Mz2 varies from 555 GeV to 620 GeV and (m
t) CDF = 175.6 ± 5.7 GeV (Table 1): (a) SNew varies from -0.100 ± 0.089 to -0.130 ± 0.090, (b) TNew varies from -0.098 ± 0.097 to -0.129 ± 0.098, (c) UNew varies from -0.229 ± 0.177 to -0.253 ± 0.206, (d) Τz varies from 2.487 ± 0.027 to 2.486 ± 0.027, (e) ALR varies from 0.0125 ± 0.0003 to 0.0126 ± 0.0003, (f) A
FB
b
remains constant at 0.0080 ± 0.0007. Almost identical values are obtained for (m
t)D0 = 169 GeV (see table 2). (ii) Triple gauge boson vertices (TGV) contributions: AsMz
2 varies from 555 GeV to 620 GeV and (m
t) CDF = 175.6 ±5.7 GeV. (a)√s = 500 GeV, asymptotic case:
varies from -0.301 to -0.179;
varies from -0.622 to -0.379;
varies from +0.0061 to 0.0056;
varies from -3.691 to -2.186.
varies from +0.270 to +0.118;
varies from +0.552 to 0.238;
varies from +0.0004 to +0.0002;
remains constant at -0.110. (b)√s = 700 GeV, asymptotic case:
varies from -0.297 to -0.176;
varies from -0.609 to -0.370;
varies from -0.0082 to -0.0078;
varies from -3.680 to -2.171.√s = 700 GeV, nonasymptotic case:
varies from -0.173 to -0.299;
varies from-0.343 to -0.591;
varies from -0.005 to -0.011;
remains constant at -0.110.
The pattern of form factors values for√s = 1000, 1200 GeV is almost identical to that of√s= 700 GeV. Further the values of the form factors for (m
t)D0 (=169 GeV) follow identical pattern as that of (m
t) CDF form factors values (see tables 5, 6, 9, 10).
We conclude that the values of all the form factors with the exception of these of
,
are comparable or larger than theS, T values and therefore the TGV contributions are important while deciding the use of extraU (1) model for doing physics beyond standard model. 相似文献
15.
Malcolm Ludvigsen 《General Relativity and Gravitation》1989,21(12):1205-1212
Given the news function
of a radiating space-time describing an isolated source, one can construct two physically important functions on the infinite celestial sphere surrounding the source:
相似文献
16.
Ola Bratteli 《Letters in Mathematical Physics》1982,6(6):499-504
Let δ be a quasi-free derivation of the CAR algebra, and let
be a closed *-derivation which is an extension of δ. We use Price's techniques from [6] to show that if the polynomials in
the linear field operators a(f)→a
*
(f) in D(
) is a core for
, then
is quasi-free. 相似文献
17.
R. Shimizu 《Applied Physics A: Materials Science & Processing》1979,18(4):425-426
The statistics of the sputtering process, which has been used to explain sputterbroadening effect due to surface roughness,
has been treated with conditional probabilities. This results in the relationship,
, instead of
derived by S. Hofmann [Appl. Phys.9, 59 (1976)], where δz,z, and
are the depth resolution, sputtered depth and sputtering yield, respectively. 相似文献
18.
KN sigma commutator has been calculated in the framework of the (6,
)+(
, 6) model. It is found that though this model could not be discarded in favour of the (3,
)+(
, 3) or (8, 8) model, a very large value forKN sigma term is required to get a positive value ofπN sigma term. 相似文献
19.
G.Ya. Korenman 《Hyperfine Interactions》1999,119(1-4):227-233
Effect of medium density on shift and broadening of (
) spectral lines is considered in the framework of binary-collision approximation with an effective (
)–He potential including the long-range attraction and short-range repulsion. Quantum calculations of the scattering phase
shifts at reasonable values of the potential parameters allow to explain the main features of the observed density effect
on the shape of (
) spectral lines in low-temperature helium.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
20.
B. I. Deutch 《Hyperfine Interactions》1992,73(1-2):175-191
The main suggested routes for atomic antihydrogen (
) formation will be reviewed in a pedestrian fashion. These are the following reactions:
, and (iii)
. The present status of the projects related to these reactions, as well as the projects' experimental scope, will also be
discussed or referred to. Some speculations will be made regarding the physics that can be yielded by an antihydrogen probe. 相似文献
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