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1.
Structural and electronic properties of self-assembled monolayer with 4-(4-amino-phenylazo) benzoic acid (APABA) on the Si(0 0 1)-(4 × 2) surface are investigated by ab initio calculation based on density functional theory. For the APABA chemisorption on the silicon surface, we have assumed two different binding sites: (i) amino group of molecule and (ii) carboxyl group of molecule. Considering amino-site, we have assumed two possible models for the chemisorption of molecules on the Si(0 0 1)-(4 × 2) surface: (i) an intrarow position between two neighboring Si dimers in the same dimer row (Model I), (ii) on-dimer position (Model II). We have found that Model II is 1.10 eV energetically more favorable than Model I. The Si-N bond length was calculated as 1.85 Å which is in excellent agreement with the sum of the corresponding covalent radii of 1.87 Å. Considering carboxyl-site, we have assumed exactly the same model as mentioned above. Again we have found that Model II is energetically favorable than Model I. The calculated bond lengths for Si-O and O-C are 1.76 and 1.35 Å, respectively.  相似文献   

2.
Image distortion due to weak gravitational lensing is examined using a non-perturbative method of integrating the geodesic deviation and optical scalar equations along the null geodesics connecting the observer to a distant source. The method we develop continuously changes the shape of the pencil of rays from the source to the observer with no reference to lens planes in astrophysically relevant scenarios. We compare the projected area and the ratio of semi-major to semi-minor axes of the observed elliptical image shape for circular sources from the continuous, thick-lens method with the commonly assumed thin-lens approximation. We find that for truncated singular isothermal sphere and NFW models of realistic galaxy clusters, the commonly used thin-lens approximation is accurate to better than 1 part in 104 in predicting the image area and axes ratios. For asymmetric thick lenses consisting of two massive clusters separated along the line of sight in redshift up to Δz = 0.2, we find that modeling the image distortion as two clusters in a single lens plane does not produce relative errors in image area or axes ratio more than 0.5%.  相似文献   

3.
We have investigated the ferromagnetic resonance (FMR) response of as-made and temperature annealed FePt magnetic nanoparticles. The as-made nanoparticles, which have been fabricated by a chemical route, crystallize in the low magnetic anisotropy fcc phase and have a diameter in the range of 2-4 nm. The annealing of the particles at high temperatures (TA=550, 650 and C) in an inert Ar atmosphere produces a partial transformation to the high magnetocrystalline anisotropy L10 phase, with a significant increase in particle size and size distribution. FMR measurements at X-band (9.5 GHz) and Q-band (34 GHz) show a single relatively narrow line for the as-synthesized particles and a structure of two superimposed lines for the three annealed samples. The origin of this line shape has been attributed to the presence of the disordered fcc phase. Assuming that the system consists of a collection of identical particles with a random distribution of easy axes, we have been able to estimate a mean value for the magnetic anisotropy constant of the particles in the fcc phase, K∼2×106 erg/cm3. The measured line shape in the annealed samples can be explained if we consider that the magnetic anisotropy of the particles has a gaussian distribution with a relatively broad width.  相似文献   

4.
5.
Laser ablation technology is used to isolate magnetic material to generate a local magnetic field effect. The impact of an induced magnetic field is enhanced by using the external magnetic field and can be widely employed to collect magnetic particles and position biomolecular in the bio-examination field. In addition, the magnetic field is affected and induced by the thermal stress produced after energy is exerted on the materials. Therefore, this study presents the phase of induced magnetic field (PIMF) of ferromagnetic film (Ni—1-μm thick) isolated using a 355-nm pulsed ultraviolet laser. In the experiment, three patterns comprising the following shapes and various isolated angle were designed for testing: hexagon (type I, 120°), L shape (type II, 90°), and cross shape (type III, 90°). The magnetic force microscopy image showed that when the isolating angle decreased, the PIMF increased, the value of which at the periphery of the corner of the type I and II patterns was ?3.96° and ?4.09°, respectively. In addition, by increasing the ablation time and residual thermal stress remaining in the material to increase the impact of the material’s properties when laser scanning speed was reduced from 1,000 to 500 mm/s, the PIMF value increased from ?4.09° to ?5.82°. The PIMF value of the type III pattern increased to ?9.87° because the residual thermal stress was twice that of the type II pattern. In the future, the experimental results can be used as a helpful reference for controlling magnetic particles in biomedical chips.  相似文献   

6.
To investigate the effects of multiple anisotropies, morphology and size on magnetic properties of fine particles, cobalt-modified materials with different shapes were tested at temperatures from liquid nitrogen to 400 K. Some interesting and original conclusions were drawn: (a) When multiple easy axes are available, thermal fluctuations can induce the magnetization to switch from one axis to the other; the overall effect will be an increase of the fraction of particles with superparamagnetic behaviour. (b) The phenomenon will be greater for materials where the conflicting anisotropy constants are similar (isotropic particles); thus, for a given composition, the lower the shape anisotropy and the larger the superparamagnetic fraction. (c) Porosity and particle defects will contribute to increase the super-paramagnetic fraction. (d) In practical media (tapes) the effect of the superparamagnetic fraction is much lower than expected: a “constricted magnetization” phenomenon could account for such behaviour. (e) The lack of interactions predicted for truly isotropic media is experimentally verified only at extremely low temperatures. (f) Partial orientation in the plane of the strongest anisotropy axis must be taken into account for explaining the behaviour of SFD; under such assumption, “quasi-spherical” particles will behave quite differently from elongated ones. (g) Rotational hysteresis, CF and (1 ? S1) for isotropic particles seems to indicate that the rotational mechanism might not be accounted for by known models.  相似文献   

7.
受电子器件工作频率及功率的限制,传统电子学方法产生的噪声源的超噪比通常小于20 dB,针对这一问题,本文提出了一种基于非相干光拍频产生高超噪比宽带毫米波噪声技术.首先,用两个光滤波器对宽带放大自发辐射光源进行滤波整形.将获得的两束频率不同的放大自发辐射光耦合进入光电探测器进行拍频,从而产生电噪声信号.理论分析发现,通过...  相似文献   

8.
The rotation patterns of the 133Cs (I=7/2) nuclear magnetic resonance (NMR) in a Cs2ZnCl4 single crystal grown by using the slow evaporation method were measured in two mutually perpendicular crystal planes. Two different groups of Cs resonances were recorded; this result points to the existence of two types of crystallographically inequivalent Cs(I) and Cs(II). The angular dependences of the NMR spectra led to different values for the quadrupole coupling constants and asymmetry parameters: e2qQ/h=148 kHz and η=0.11 for the Cs(I) ion, and e2qQ/h=274 kHz and η=0.66 for the Cs(II) ion. The EFG tensors of Cs(I) and Cs(II) are asymmetric, and the orientations of the principal axes of the EFG tensors do not coincide. Only, the principal Y-axes of the EFG tensors coincide for the Cs(I) and Cs(II) sites. The Cs(I) ion is surrounded by 11 chlorine ions, making it rather free and high in symmetry. The Cs(II) ion has only nine neighbors and seems to be more tight than the Cs(I) ion.  相似文献   

9.
The static magnetic structure of a single shape-defective Ni80Fe20 nanowire has been investigated by magnetic force microscopy (MFM). The result shows that defects of the shape of the nanowire have an effect on the magnetic state of the nanowire. In order to check the influence of defects of the shape on the magnetic state, a micromagnetic simulation and a MFM image simulated computation are introduced. Two model systems are studied: (I) model?I: no defects of the shape is present and (II) model?II: the defects of the shape are introduced into the ends of the nanowire. The simulated computation result of model?II is in good agreement with experimental results for the single Ni80Fe20 nanowire. It may have important significance for guiding in sample preparation and application.  相似文献   

10.
Laser-induced desorption of metal atoms from the surface of small metal particles has been investigated as a function of the shape of the particles and the polarization of the incident laser light. The particles were supported on LiF, quartz or sapphire substrates. In a first set of experiments, the shape of the particles was determined by recording optical transmission spectra with s- and p-polarized light incident under an angle of typically 40° with respect to the surface normal. The metal particles turn out to be oblate, the ratio of the axes perpendicular and parallel to the substrate surface being on the order of 0.5. This ratio decreases with increasing particle size. Also, the particles change shape if the temperature is raised. In further experiments, s- and p-polarized light has been used to stimulate desorption of atoms via surface plasmon excitation. It is found that the desorption rate markedly depends on the polarization of the light. This is explained by excitation of the collective electron oscillation along different axes of the non-spherical particles.  相似文献   

11.
Recent interest in the study of stacking faults and non-basal slip in Mg alloys is partly based on the argument that these phenomena positively influence mechanical behaviour. Inspection of the published literature, however, reveals that there is a lack of fundamental information on the mechanisms that govern the formation of stacking faults, especially I1-type stacking faults (I1 faults). Moreover, controversial and sometimes contradictory mechanisms have been proposed concerning the interactions between stacking faults and dislocations. Therefore, we describe a fundamental transmission electron microscope investigation on Mg 2.5 at. % Y (Mg–2.5Y) processed via hot isostatic pressing (HIP) and extrusion at 623 K. In the as-HIPed Mg–2.5Y, many 〈c〉 and 〈a〉 dislocations, together with some 〈c + a〉 dislocations were documented, but no stacking faults were observed. In contrast, in the as-extruded Mg–2.5Y, a relatively high density of stacking faults and some non-basal dislocations were documented. Specifically, there were three different cases for the configurations of observed stacking faults. Case (I): pure I2 faults; Case (II): mixture of I1 faults and non-basal dislocations having 〈c〉 component, together with basal 〈a〉 dislocations; Case (III): mixture of predominant I2 faults and rare I1 faults, together with jog-like dislocation configuration. By comparing the differences in extended defect configurations, we propose three distinct stacking fault formation mechanisms for each case in the context of slip activity and point defect generation during extrusion. Furthermore, we discuss the role of stacking faults on deformation mechanisms in the context of dynamic interactions between stacking faults and non-basal slip.  相似文献   

12.
133Cs (I=7/2) nuclear magnetic resonance in a Cs2CuCl4 single crystal grown by using the slow evaporation method was measured in its three mutually perpendicular crystal planes. The 133Cs resonances of two different groups with two crystallographically inequivalent cesium nuclei, Cs(I) and Cs(II), in the unit cell were recorded. The transferred hyperfine fields for Cs(I) and Cs(II) calculated from the paramagnetic shift and the molecular susceptibility measurements could be expressed by the linear equation Hhf=AT+B. The angular dependence of the 133Cs nuclear magnetic resonance spectra showed that the Cs(I) and the Cs(II) nuclei had different values for the quadrupole coupling constant. The electric field gradient tensors of Cs(I) and Cs(II) were symmetric, and the orientations of their principal axes did not coincide. The Cs(I) ion surrounded by 11 chlorine ions had a small quadrupole parameter, a smaller charge distribution, and a small value for the transferred hyperfine field. However, the Cs(II) ion surrounded by nine chlorine ions had a larger quadrupole parameter, a larger charge distribution, and a larger value for the transferred hyperfine field.  相似文献   

13.
We consider a version of random motion of hard core particles on the semi-lattice 1,2,3,… , where in each time instant one of three possible events occurs, viz., (a) a randomly chosen particle hops to a free neighboring site, (b) a particle is created at the origin (namely, at site 1) provided that site 1 is free and (c) a particle is eliminated at the origin (provided that the site 1 is occupied). Relations to the BKP equation are explained. Namely, the tau functions of two different BKP hierarchies provide generating functions respectively (I) for transition weights between different particle configurations and (II) for an important object: a normalization function which plays the role of the statistical sum for our non-equilibrium system. For time t→∞ we obtain the asymptotic configuration of particles obtained from the initial empty state (the state without particles).  相似文献   

14.
We present in this study computational simulations of the ferromagnetic resonance response of magnetic nanoparticles with a uniaxial anisotropy considerably larger than the microwave excitation frequency (in field units). The particles are assumed to be randomly oriented in a two dimensional lattice, and are coupled by dipolar interactions through an effective demagnetization field, which is proportional to the packing fraction. We have included in the model fluctuations in the anisotropy field (HK) and allowed variations in the demagnetizing field. We then analyzed the line shape and line intensity as a function of both fields. We have found that when HK is increased the line shape changes drastically, with a structure of two lines appearing at high fields. The line intensity has a maximum when HK equals the frequency gap and decreases considerably for larger values of the anisotropy. The effects of fluctuations in HK and variations in the packing fraction have been also studied. Comparison with experimental data shows that the overall observed behavior is dominated by the particles with lower anisotropy.  相似文献   

15.
Current approaches for assessing a confocal micro-X-rayfluorescence–probing volume involve the use of sharp knife edges, thin films, or wires, which are moved through this volume. The fluorescence radiation excited in the material of the object is measured, and profiles are built to enable the determination of the full width at half maximum in any of the three axes of the excited volume. Such approaches do not provide information on the shape of the volume, and the consequent alignment of both used lenses is made based on the position of the maxima of the registered intensity measurements. The use of particles that are smaller than the interaction volume (isolated enough to prevent the influence of nearby particles) and translated through the interaction volume (3D scan) is presented as an alternative methodology to determine the confocal probing volume. Spherical shaped uranium particles with diameter of 1–3 μm originally produced for scanning electron microscopy analysis calibration purposes were used in this study. The results obtained showed that the effectively probed confocal volume has a distinct prolate spheroidal shape that is longer in the axis of the confocal detector than it is wide on the axes of the plane perpendicular to it. The diameter in the longest axis (tilted accordingly to the angle between the two silicon drift detectors) was found to be approximately 25 μm, whereas the shorter was found about 15 μm each, with a volume of about 3,000 μm3.  相似文献   

16.
With toy modelling of conceptual aspects of quantum cosmology and the problem of time in quantum gravity in mind, I study the classical and quantum dynamics of the pure-shape (i.e. scale-free) triangle formed by 3 particles in 2-d. I do so by importing techniques to the triangle model from the corresponding 4 particles in 1-d model, using the fact that both have 2-spheres for shape spaces, though the latter has a trivial realization whilst the former has a more involved Hopf (or Dragt) type realization. I furthermore interpret the ensuing Dragt-type coordinates as shape quantities: a measure of anisoscelesness, the ellipticity of the base and apex’s moments of inertia, and a quantity proportional to the area of the triangle. I promote these quantities at the quantum level to operators whose expectation and spread are then useful in understanding the quantum states of the system. Additionally, I tessellate the 2-sphere by its physical interpretation as the shape space of triangles, and then use this as a back-cloth from which to read off the interpretation of dynamical trajectories, potentials and wavefunctions. I include applications to timeless approaches to the problem of time and to the role of uniform states in quantum cosmological modelling.  相似文献   

17.
Many copper containing proteins exhibit well defined ESEEM signals detected at X-band and C-band. In these systems the Cu(II) ion is coordinated to one or several histidine residues. The main sharp features measured in the ESEEM spectra originate from the interaction of the unpaired electron with the remote nitrogen nucleus of the histidine ring. The relative intensities of these features contain information about the orientation of the NQI-tensor in the molecular axis frame as defined by the principal axes of theg-matrix. This information can be related to the orientation of the imidazole ring in the complex. We present a systematic approach to determine the constraints of the Euler angles, α, β, ψ of the NQI-tensor in theg-matrix principal axis system. The first step is to analyze the intensity ratios of the quadrupole peaks and the line shape of the double quantum feature measured on the canonical positions in the EPR spectrum. This will lead to a constraint in the angles (α, β) as well as the effective hyperfine interaction. This information is further refined using spectra on other orientation selective positions. We have applied this method to Cu(II)-Bleomycin and two model compounds: Cu(II)-pypep and Cu(II)-PMA of which we have determined the principal quadrupole values and the orientation of the quadrupole tensor with respect to theg-matrix axis system.  相似文献   

18.
We propose two supersymmetric Standard Models (SMs) with decaying and stable dark matter (DM) particles. To explain the SM fermion masses and mixings and have a heavy decay DM particle S, we consider the Froggatt–Nielsen mechanism by introducing an anomalous U(1) X gauge symmetry. Around the string scale, the U(1) X gauge symmetry is broken down to a Z 2 symmetry under which S is odd while all the SM particles are even. S obtains a vacuum expectation value around the TeV scale, and then it can three-body decay dominantly to the second/third family of the SM leptons in Model I and to the first family of the SM leptons in Model II. Choosing a benchmark point in the constrained minimal supersymmetric SM with exact R parity, we show that the lightest neutralino DM is consistent with the CDMS II experiment. Considering S three-body decay and choosing suitable parameters, we show that the PAMELA and Fermi-LAT experiments and the PAMELA and ATIC experiments can be explained in Model I and Model II, respectively.  相似文献   

19.
The use of simplified particle shapes for modeling scattering by irregularly shaped mineral-dust particles is studied using polyhedral prisms and spheroids as model particles. Simulated phase matrices averaged over shape and size distributions at wavelength 633 nm are compared with a laboratory-measured phase matrix of feldspar particles with known size distribution with effective radius of . When an equi-probable shape distribution is assumed, prisms and oblate spheroids agree with measurements to a similar degree, whereas prolate spheroids perform markedly better. Both spheroids and prisms perform much better than spheres. When an automatic fitting method is applied for finding optimal shape distributions, it is found that the most elongated spheroids are most important for good fits, whereas nearly-spherical spheroids are generally of very little importance. The phase matrices for the different polyhedral prisms, on the other hand, are found to be similar, thus their shape-averaged phase matrices are insensitive to the shape distribution assumed. For spheroids, a simple parameterization for the shape distribution, where weights increase with increasing departure from spherical shape, is proposed and tested. This parameterization improves the fit of most phase matrix elements attained with an equi-probable shape distribution, and it performs particularly well for reproducing the measured phase function.  相似文献   

20.
We analyze the dynamics of a simple but nontrivial classical Hamiltonian system of infinitely many coupled rotators. We assume that this infinite system is driven out of thermal equilibrium either because energy is injected by an external force (Case I), or because heat flows between two thermostats at different temperatures (Case II). We discuss several possible definitions of the entropy production associated with a finite or infinite region, or with a partition of the system into a finite number of pieces. We show that these definitions satisfy the expected bounds in terms of thermostat temperatures and energy flow.  相似文献   

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