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1.
C. Monthus T. Garel 《The European Physical Journal B - Condensed Matter and Complex Systems》2006,53(1):39-45
The directed polymer in a 1+3 dimensional
random medium is known to present a disorder-induced phase
transition. For a polymer of length L, the high temperature
phase is characterized by a diffusive behavior for the end-point
displacement R2 ∼L and by free-energy fluctuations of order
ΔF(L) ∼O(1). The low-temperature phase is characterized by
an anomalous wandering exponent R2/L ∼Lω and
by free-energy fluctuations of order ΔF(L) ∼Lω
where ω∼0.18. In this paper, we first study the scaling
behavior of various properties to localize the critical temperature
Tc. Our results concerning R2/L and ΔF(L) point towards
0.76 < Tc ≤T2=0.79, so our conclusion is that Tc is equal
or very close to the upper bound T2 derived by Derrida and
coworkers (T2 corresponds to the temperature above which the ratio
remains finite as L ↦
∞). We then present histograms for the free-energy, energy and
entropy over disorder samples. For T ≫Tc, the free-energy
distribution is found to be Gaussian. For T ≪Tc, the free-energy
distribution coincides with the ground state energy distribution, in
agreement with the zero-temperature fixed point picture. Moreover the
entropy fluctuations are of order ΔS ∼L1/2 and follow a
Gaussian distribution, in agreement with the droplet predictions,
where the free-energy term ΔF ∼Lω is a near
cancellation of energy and entropy contributions of order L1/2. 相似文献
2.
T. Matulewicz L. Aphecetche Y. Charbonnier H. Delagrange K.K. Gudima G. Martınez M. Płoszajczak Y. Schutz V.D. Toneev M. Appenheimer R. Averbeck J. Dıaz A. Döppenschmidt M.J. van Goethem S. Hlavač M. Hoefman R. Holzmann F. Lefèvre A. Kugler H. Löhner A. Marın V. Metag R. Novotny R.W. Ostendorf R.H. Siemssen R.S. Simon R. Stratmann H. Ströher P. Tlusty P.H. Vogt V. Wagner J. Weiss H.W. Wilschut F. Wissmann A.R. Wolf M. Wolf 《The European Physical Journal A - Hadrons and Nuclei》2000,9(1):69-72
Proton-π0 coincidences have been measured at the beam energy of 180A MeV in the reaction Ar+Ca studied by TAPS at SIS/GSI. In the proton-π0 invariant mass spectrum we observe a significant excess of strength above the background obtained by event mixing. We attribute
this signal to the strength distribution N
Δ of the Δ baryonic resonance. No correlation is observed in the case of deuteron-π0 coincidences. Assuming isotropic emission of π0 and Δ+ from a midrapidity thermal source and isospin symmetry, we determined the global N
Δ/N
πratio of 0.79 ±0.30(stat) ±0.2(syst). This value indicates that most pions produced at subthreshold energy in heavy-ion reaction
are mediated by the Δ-resonance.
Received: 7 April 2000 / Accepted: 29 August 2000 相似文献
3.
利用边缘相位校正实现光束整形的高精度优化 总被引:2,自引:1,他引:1
提出利用边缘相位校正的新方法,校正用追迹法设计的产生环形光束的衍射光学元件的相位分布,从而实现光束整形中的高精度优化。通过将高斯光束整形为环形光束,将该方法、G-S(Gerchberg-Saxton)算法和改进的G-S算法设计得到的整形结果作了比较,结果表明,G-S算法的整形结果虽然衍射效率最大,但是均方根值和最大偏差也太大;改进的G-S算法可以有效的降低均方根值和最大偏差,但衍射效率也有较大的下降;而用边缘相位校正可以在衍射效率略微下降的情况下,更大的降低均方根值和最大偏差,其整形结果是综合了衍射效率、均方根值和最大偏差这三个评价指标以后得到的最优化结果,已接近理想的环形光束。 相似文献
4.
The statistics of the occurrence of freak waves on a surface of an ideal heavy liquid is studied. The freak (rogue, extreme)
waves arise in the course of evolution of a statistically homogeneous random Gaussian wave field. The mean steepness of initial
data varies from small (μ2 = 1.54 × 10−3) to moderate (μ2 = 3.08 × 10−3) values. The frequency of the occurrence of extreme waves decreases with an increase in the spectral width of the initial
distribution, but remains relatively high even for broad spectra (Δ
k
/Δ ∼ 1). 相似文献
5.
I. Horn A. V. Anisovich G. Anton R. Bantes O. Bartholomy R. Beck Y. Beloglazov R. Bogendörfer R. Castelijns V. Credé A. Ehmanns J. Ernst I. Fabry H. Flemming A. Fösel M. Fuchs Ch. Funke R. Gothe A. Gridnev E. Gutz S. Höffgen J. Hößl J. Junkersfeld H. Kalinowsky F. Klein E. Klempt H. Koch M. Konrad B. Kopf B. Krusche J. Langheinrich H. Löhner I. Lopatin J. Lotz H. Matthäy D. Menze J. Messchendorp V. Metag V. A. Nikonov D. Novinski M. Ostrick H. van Pee A. V. Sarantsev C. Schmidt H. Schmieden B. Schoch G. Suft V. Sumachev T. Szczepanek U. Thoma D. Walther Ch. Weinheimer 《The European Physical Journal A - Hadrons and Nuclei》2008,38(2):173-186
The reaction γp → pπ0η has been studied with the CBELSA detector at the tagged photon beam of the Bonn electron stretcher facility. The reaction
shows contributions from Δ+(1232)η , N(1535)+π0 and pa
0(980) as intermediate states. A partial-wave analysis suggests that the reaction proceeds via formation of six Δ -resonances,
Δ(1600)P
33 , Δ(1920)P
33 , Δ(1700)D
33 , Δ(1940)D
33 , Δ(1905)F
35 , Δ(2360)D
33 , and two nucleon resonances N(1880)P
11 and N(2200)P
13 , for which pole positions and decay branching ratios are given. 相似文献
6.
F. Kottmann W. Amir F. Biraben C. A. N. Conde S. Dhawan T. W. Hänsch F. J. Hartmann V. W. Hughes O. Huot P. Indelicato L. Julien P. Knowles S. Kazamias Y.-W. Liu F. Mulhauser F. Nez R. Pohl P. Rabinowitz J. M. F. dos Santos L. A. Schaller H. Schneuwly W. Schott D. Taqqu J. F. C. A. Veloso 《Hyperfine Interactions》2001,138(1-4):55-60
A measurement of the 2S Lamb shift in muonic hydrogen (μ−p) is being prepared at the Paul Scherrer Institute (PSI). The goal of the experiment is to measure the energy difference
ΔE(25
P
3/2−23
S
1/2) by laser spectroscopy (λ≈6μm) to a precision of 30 ppm and to deduce the root mean square (rms) proton charge radius with
10−3 relative accuracy, 20 times more precise than presently known.
An important prerequisite to this experiment is the availability of long-lived μp2S
-atoms. A 2S-lifetime of ∼1 μs – sufficiently long to perform the laser experiment – at H2 gas pressures of 1–2 hPa was deduced from recent measurements of the collisional 2S-quenching rate. A new low-energy negative muon beam yields an order of magnitude more muon stops in a small low-density gas
volume than a conventional cloud muon beam. A stack of ultra-thin carbon foils is the key element of a fast detector for keV-muons.
The development of a 2 keV X-ray detector and a 3-stage laser system providing 0.5 mJ laser pulses at 6 μm is on the way.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
7.
Pulse shape discrimination (PSD) with totally depleted transmission type Si surface barrier detector in reverse mount has
been investigated to identify fission fragments in the presence of elastic background in heavy ion-induced fission reactions
by both numerical simulation and experimental studies. The PSD method is compared with the other conventional methods adopted
to identify fission fragments with solid-state detectors such as ΔE–E telescope and single thin ΔE detector and the data for the10B +232Th fission reaction are presented. Results demonstrate the usefulness of a single transmission-type surface barrier detector
for the identification of fission fragments and projectiles like heavy ions 相似文献
8.
According to recent progresses in the finite size scaling theory of
disordered systems, thermodynamic observables are not self-averaging
at critical points when the disorder is relevant in the
Harris criterion sense. This lack of
self-averageness at criticality is directly related to the distribution
of pseudo-critical temperatures Tc(i,L) over the ensemble of
samples (i) of size L. In this paper, we apply this analysis to
disordered Poland-Scheraga models with different loop exponents c,
corresponding to marginal and relevant disorder. In all cases, we
numerically obtain a Gaussian
histogram of pseudo-critical temperatures Tc(i,L) with mean
Tcav(L) and width ΔTc(L).
For the marginal case c=1.5 corresponding to two-dimensional wetting,
both the width ΔTc(L) and the shift
[Tc(∞)-Tcav(L)] decay as L-1/2, so the exponent is
unchanged (νrandom=2=νpure) but disorder is relevant and
leads to non self-averaging at criticality.
For relevant disorder
c=1.75, the width ΔTc(L) and the shift
[Tc(∞)-Tcav(L)] decay with the same new exponent
L-1/νrandom (where νrandom ∼2.7 > 2 > νpure) and
there is again no self-averaging at criticality. Finally for the value
c=2.15, of interest in the context of DNA denaturation, the
transition is first-order in the pure case. In the presence of
disorder, the width ΔTc(L) ∼L-1/2
dominates over the shift [Tc(∞)-Tcav(L)] ∼L-1,
i.e. there are two correlation length exponents ν=2 and
that govern respectively the averaged/typical loop distribution. 相似文献
9.
It is shown that high-accuracy contact-free measurements of the divergence and emittance of an accelerated H− ion beam at the exit from the source can in principle be performed by passive Doppler spectroscopy of a beam of excited hydrogen
atoms produced by neutralization of the ions with excitation on the residual gas in the source channel. The intensity of the
Hα-line radiation detected by the Doppler system is calculated, taking into account the principal processes leading to the excitation
and deexcitation of the 3s, 3p, and 3d levels of the hydrogen atoms in the beam, for residual gas densities of the order of 10−4–10−5 Torr in the source channel. The computed Hα-line intensity was confirmed experimentally, making it possible to perform photoelectronic detection of the spectral contour
of the line in the current mode rather than the photon-counting mode.
Zh. Tekh. Fiz. 68, 15–18 (June 1998) 相似文献
10.
The values of the insulator gap Δ in one-dimensional systems of interacting bosons described by the Hubbard Hamiltonian are
calculated at low temperatures by the quantum world-line Monte Carlo algorithm. The dependence of Δ on the size of the system,
the temperature, and the parameters of the model is investigated. It is shown that a chain with N
a=50 sites is already sufficient to estimate the thermodynamic value of the critical quantity (t/U)c for which a transition from the insulator into the superfluid state occurs in a commensurate system. To within the computational
error, this value, (t/U)c=0.300±0.005, agrees with the value (t/U)c=0.304±0.002 obtained previously by the combined “exact diagonalization + renormalization-group analysis” method. The characteristic
Kosterlitz-Thouless behavior of the insulator gap is demonstrated near the critical region: Δ∼exp[−b(1−t/t
c)−1/2].
Pis’ma Zh. éksp. Teor. Fiz. 64, No. 2, 92–96 (25 July 1996) 相似文献
11.
P. Boolchand D. McDaniel C. Blue Y. Wu R. Enzweiler K. Elgaid R. Burrows 《Hyperfine Interactions》1992,68(1-4):15-25
A new symmetric Fe3+ site (labelled E) (δ=0.28(2) mm/s and Δ=0.15 mm/s) is observed in the R1Ba2Cu3O7 family of superconductors for R=Y and Eu. The decay and growth of site E are established in two seemingly unrelated experiments,
one as a function of room temperature aging for R=Y, and the other as a function of oxygen loading at elevated temperatures
and pressures for R=Eu. In each experiment, the results show that site E is genetically related to the well documented chainsites
A(Δ=1.9 mm/s), C(Δ=1.1 mm/s) and D(Δ=1.6 mm/s). We propose that site E represents a quasi-octahedral chain-site having pairs
of O(1), O(4) and O(5) nearestneighbor oxygen sites. The two remaining doublets, B(Δ≈0.4 mm/s) and B′(Δ=0.78 mm/s) represent
Fe3+ dopant sites present in the all-important CuO2 planes, possessing coordination numbers of 6 and 5, respectively. 相似文献
12.
The thermo-emf ΔV and thermoelectric current ΔI generated by imposing a temperature gradient alternating at a period of T on a thermoelectric (TE) generator were measured as a function of t, where t is the lapsed time and 1/T was varied from 0 to 1/30 s-1. A TE generator was sandwiched between two Peltier modules connected in series. The alternating temperature gradients were produced by imposing an alternating voltage V on two Peltier modules, where V was varied from 1.0 to 3.7 V. Both ΔV and ΔI generated by the TE generator oscillate at a period of T but their amplitudes tend to increase monotonically with an increase of V. The effective thermo-emf ΔVeff and current ΔIeff calculated from ΔV and ΔI increase abruptly with an increase of 1/T and have a local maximum at 1/T=1/120 or 1/240 s-1. The generating power ΔWeff(=ΔVeffΔIeff) tends to increase proportionally with an increase of input power Winput, owing to the increase in the temperature difference. The rate of ΔWeff to Winput at 1/T=1/240 s-1 reached approximately 3.2 times as large as that obtained for the steady temperature gradient corresponding to 1/T=0 s-1. It was thus found that the generating power of the TE generator operating under the temperature gradient alternating at an optimum period is remarkably increased compared to that of a TE generator working under a conventional steady temperature gradient. PACS 72.15.Jf; 84.60.Rb; 85.30De 相似文献
13.
Khusniddin K. Olimov Mahnaz Q. Haseeb Alisher K. Olimov Imran Khan 《Central European Journal of Physics》2011,9(6):1393-1409
The production of Δ0(1232)-resonances in p+12C collisions at 4.2 GeV/c was analyzed with 4π acceptance. The mass distribution of Δ0(1232) was reconstructed using an angular criterion. The fraction of charged π
−-mesons coming from Δ0(1232) decay was estimated and compared to those obtained in earlier works. The momentum, transverse momentum, kinetic energy,
and rapidity distributions as well as invariant cross sections of Δ0(1232)-resonances were reconstructed in the laboratory frame. The mean kinematical characteristics of the reconstructed Δ0(1232) were compared to those of participant protons in experiment and within some of the models. The freeze-out temperature
of Δ0(1232) estimated in the present analysis was compared with those obtained using different methods for Δ(1232) produced with
other sets of colliding nuclei at various incident energies. The relative number of nucleons excited to Δ0 (1232) at freeze-out conditions in p+12C collisions was estimated. 相似文献
14.
Jiahong Wu 《Communications in Mathematical Physics》2006,263(3):803-831
When estimating solutions of dissipative partial differential equations in Lp-related spaces, we often need lower bounds for an integral involving the dissipative term. If the dissipative term is given
by the usual Laplacian −Δ, lower bounds can be derived through integration by parts and embedding inequalities. However, when
the Laplacian is replaced by the fractional Laplacian (−Δ)α, the approach of integration by parts no longer applies. In this paper, we obtain lower bounds for the integral involving
(−Δ)α by combining pointwise inequalities for (−Δ)α with Bernstein's inequalities for fractional derivatives. As an application of these lower bounds, we establish the existence
and uniqueness of solutions to the generalized Navier-Stokes equations in Besov spaces. The generalized Navier-Stokes equations
are the equations resulting from replacing −Δ in the Navier-Stokes equations by (−Δ)α. 相似文献
15.
Suresh Chandra 《Pramana》2005,65(6):1133-1137
Statement of Kaur and Mahajan [1] about the definition of Δ used by Chandra [2] is not correct. Even if we take Δ = μω
e
2
r
e
2
/2De, the relation between Δ and G(=8ωexe/Be) is obtained as Δ = 4.21452856G, provided the vibrational energy of a diatomic molecule is expressed in terms of limited
Dunham coefficients, Y10, Y20, Y01 and Y11. This relation is still different from that of Kaur and Mahajan [3] 相似文献
16.
P. S. Antsiferov 《Central European Journal of Physics》2003,1(2):268-288
The article presents the results of a study of characteristic X-ray spectra of free atoms by means of a new simple technique.
A pulsed electron beam was used for evaporation and to create inner-shell vacancies in free atoms of metals. The spectra were
obtained with the help of an X-ray monochromator which allowed precise comparison between the free-atoms spectra and corresponding
solid-state spectra. The shifts of the peaks were measured and found to be in the range Δλ/λ≈10−5–10−4. The K-, L- and M-series spectra were studied. A number of the free-atoms spectra revealed structure which was not resolved
in the solid-state spectra and which is of interest for atomic structure calculation applications. This electron beam technique
for the investigation of X-ray characteristic spectra of free atoms can be used for the refinement of X-ray wavelength standards. 相似文献
17.
By using the second-order moment of the power density, the beam width, far-field divergence angle and M2 factor of nonparaxial truncated flattened Gaussian (FG) beams are derived analytically. It is shown that the M2 factor of nonparaxial truncated FG beams depends not only on the truncation parameter δ and beam order N, but also on the initial waist-width to wavelength ratio w0/λ. The far-field divergence angle approaches an asymptotic value of θmax=63.435° when the truncation parameter δ → 0. For the special cases of N = 0 and δ → ∞ our results reduce to those of nonparaxial truncated Gaussian beams and nonparaxial untruncated FG beams, respectively. 相似文献
18.
A sequential three-dimensional (3D) particle-in-cell simulation code PICPSI-3D with a user friendly graphical user interface
(GUI) has been developed and used to study the interaction of plasma with ultrahigh intensity laser radiation. A case study
of laser–plasma-based electron acceleration has been carried out to assess the performance of this code. Simulations have
been performed for a Gaussian laser beam of peak intensity 5 × 1019 W/cm2 propagating through an underdense plasma of uniform density 1 × 1019 cm − 3, and for a Gaussian laser beam of peak intensity 1.5 × 1019 W/cm2 propagating through an underdense plasma of uniform density 3.5 × 1019 cm − 3. The electron energy spectrum has been evaluated at different time-steps during the propagation of the laser beam. When the
plasma density is 1 × 1019 cm − 3, simulations show that the electron energy spectrum forms a monoenergetic peak at ~14 MeV, with an energy spread of ±7 MeV.
On the other hand, when the plasma density is 3.5 × 1019 cm − 3, simulations show that the electron energy spectrum forms a monoenergetic peak at ~23 MeV, with an energy spread of ±7.5 MeV. 相似文献
19.
Amorphous structure generated by mechanical alloying (MA) is often used as a precursor for generating nanocomposites through
controlled devitrification. The amorphous forming composition range of ternary Al-Ni-Ti system was calculated using the extended
Miedema’s semi-empirical model. Eleven compositions of this system showing a wide range of negative enthalpy of mixing (−ΔH
mix) and amorphization (−ΔH
amor) of the constituent elements were selected for synthesis by MA. The Al88Ni6Ti6 alloy with relatively small negative ΔH
mix (−0.4 kJ/mol) and ΔHamor (−14.8 kJ/mol) became completely amorphous after 120 h of milling, which is possibly the first report of complete amorphization
of an Al-based rare earth element free Al-TM-TM system (TM = transition metal) by MA. The alloys of other compositions selected
had much more negative ΔHmix and Hamor; but they yielded either nanocomposites of partial amorphous and crystalline structure or no amorphous phase at all in the
as-milled condition, evidencing a high degree of stability of the intermetallic phases under the MA environment. Hence, the
negative ΔH
mix and ΔH
amor are not so reliable for predicting the amorphization in the present system by MA 相似文献
20.
Coherent propagation of atomic-matter waves in a one-dimensional optical lattice is studied. Wave packets of cold two-level
atoms propagate simultaneously in two optical potentials in a dressed-state basis. Three regimes of the wave-packet propagation
are specified by the quantity Δ2
/ω
D
, where Δ and ω
D
are the dimensionless atom–laser detuning and the Doppler shift, respectively. At Δ2
/ω
D
≫ 1, the propagation is essentially adiabatic, at Δ2
/ω
D
≪ 1, it is (almost) resonant, and at Δ2 ≃ ω
D
, the wave packets propagate nonadiabatically, splitting at each node of the standing wave. The latter means that the atom
makes a transition from one potential to the other one when crossing each node, and the probability of that transition is
given by a Landau–Zener-like formula. All the regimes of propagation are studied with δ-like and Gaussian wave packets in the momentum and position spaces. Varying the control parameters, we can create wave packets
trapped in a well of optical potentials and moving ballistically in a given direction in close analogy with point-like atoms.
Within some range of the parameters, we force the atom to move in a pure quamtum-mechanical manner in such a way that a part
of the packet is trapped in a well, and the other part propagates ballistically. The propagation modes are found to be characterized
by different types of time evolution of the uncertainty product and the Wigner function. 相似文献