Investigation of final-stage sintering of various microsize structures prepared by micro powder injection molding

Micro powder injection molding (μPIM) has been developed as a potential technique for mass production of microcomponents in microsystems due to its shaping complexity at low cost, in which sintering is a crucial step to dictate the final properties of the microcomponents. In this paper, final-stage sintering behavior of 316L stainless steel microsize structures prepared by μPIM, φ100 μm and φ60 μm, respectively, was studied. The effect of size reduction in the regime of micrometers on the density of various microsize structures was investigated. Sintering kinetics of the microsize structures of φ100 μm and φ60 μm were studied based on particle level sintering models. It is found that the microsize structures of φ60 μm had higher density than the microsize structures of φ100 μm given the same sintering condition. The results indicate that size reduction in the regime of micrometers facilitated densification of microsize structures. The grain growth mechanism of microsize structures varied with size. Whereas the grain growth of the microsize structures of φ100 μm is governed by surface-diffusion-controlled pore drag, the grain growth of the microsize structures of φ60 μm is controlled by boundary diffusion. During densification, the microsize structures, φ100 μm and φ60 μm, are both controlled by lattice diffusion. The corresponding activation energies are reported in the paper.     

Hot electron plasmas trapped in helical magnetic surfaces

Experimental studies on nonneutral (pure electron) plasmas of finite temperature, trapped in helical closed magnetic surfaces have been conducted. The helical electron plasmas are produced with thermal electrons launched from the outside of the last closed flux surface (LCFS). About 150 μs after the electron injection, the plasmas reach equilibrium state. Around the LCFS, a steep gradient of plasma space potential φ _s is formed. The corresponding radial electric field is about 2.5 kV/m. On the other hand, around the magnetic axis of helical magnetic surfaces, φ _s is almost constant, indicating that there are little electrons there. The volume-averaged electron density is on the order of 10¹³ m^–3, smaller than the Brillouin density limit. The confinement time seems to be limited by a disruptive instability, and is so far about 1.5 ms.      

Composite model of gauge bosons in electroweak interactions

We consider a simple Lagrangian which is constructed by only the preon and antipreon fields. By introducing the auxiliary fields φ_μ, φ _μ ^† , and ϕ_μ, it is shown that φ_μ, φ _μ ^† , and ϕ_μ correspond to the electroweak gauge bosonsW _μ ⁺ ,W _μ ⁻ , andW _μ ³ , respectively, which are composite particles of preons and antipreons.     

Cosmological Spacetimes Balanced by a Weyl Geometric Scale Covariant Scalar Field

A Weyl geometric approach to cosmology is explored, with a scalar field φ of (scale) weight −1 as crucial ingredient besides classical matter. Its relation to Jordan-Brans-Dicke theory is analyzed; overlap and differences are discussed. The energy-stress tensor of the basic state of the scalar field consists of a vacuum-like term Λg _{μ ν} with Λ depending on the Weylian scale connection and, indirectly, on matter density. For a particularly simple class of Weyl geometric models (called Einstein-Weyl universes) the energy-stress tensor of the φ-field can keep space-time geometries in equilibrium. A short glance at observational data, in particular supernovae Ia (Riess et al. in Astrophys. J. 659:98ff, 2007), shows encouraging empirical properties of these models.     

Study of Bs→φ?+?? decay in a single universal extra dimension model

Using form factors derived from the light-cone sum rules, we investigate B _s →φℓ ⁺ ℓ ⁻ (ℓ=e,μ,τ) in a single universal extra dimension model (UED). In UED, there is only one new parameter with respect to the Standard Model (SM), which is the inverse of the compactification radius R of the extra dimension. In this work, the branching ratios, the dilepton invariant mass spectra, the forward–backward asymmetries, and the lepton polarization asymmetries of B _s →φℓ ⁺ ℓ ⁻ are calculated. For a lower value of 1/R, there are some considerable discrepancies between the UED and SM. However, with the increase of 1/R, the effect of UED tends to diminish; in particular for 1/R≥1000 GeV, two models have approximately the same predictions. Compared with data from CDF for B _s →φμ ⁺ μ ⁻, we find that the 1/R tends to be larger than 350 GeV. We also find that the zero crossing point of the forward–backward asymmetry of B _s →φμ ⁺ μ ⁻ becomes smaller, which would be an important platform for probing the UED effect. These results could be tested in the Large Hadron Collider (LHC) at CERN and the future super-B factory.     

Measurement of the Temperature Dependence of the ddμ-Molecule Formation Rate in Dense Deuterium at Temperatures 300–800 K

Muon catalyzed fusion in deuterium was studied by the MCF collaboration at JINR phasotron. The measurements were carried out with a high-pressure deuterium target at the JINR phasotron in the temperature range 300–800 K at densities ≃0.5 LHD. The first experimental results for ddμ-molecule formation rate λ _ddμ in the temperature range 400–800 K with deuterium density 0.5 LHD are presented. This revised version was published online in August 2006 with corrections to the Cover Date.     

Weak Power-Counting Theorem for the Renormalization of the Nonlinear Sigma Model in Four Dimensions

The formulation of the non linear σ-model in terms of flat connection allows the construction of a perturbative solution of a local functional equation by means of cohomological techniques which are implemented in gauge theories. In this paper we discuss some properties of the solution at the one-loop level in D = 4. We prove the validity of a weak power-counting theorem in the following form: although the number of divergent amplitudes is infinite only a finite number of counterterms parameters have to be introduced in the effective action in order to make the theory finite at one loop, while respecting the functional equation (fully symmetric subtraction in the cohomological sense). The proof uses the linearized functional equation of which we provide the general solution in terms of local functionals. The counterterms are expressed in terms of linear combinations of these invariants and the coefficients are fixed by a finite number of divergent amplitudes. These latter amplitudes contain only insertions of the composite operators φ₀ (the constraint of the non linear σ-model) and F _μ (the flat connection). The structure of the functional equation suggests a hierarchy of the Green functions. In particular once the amplitudes for the composite operators φ₀ and F _μ are given all the others can be derived by functional derivatives. In this paper we show that at one loop the renormalization of the theory is achieved by the subtraction of divergences of the amplitudes at the top of the hierarchy. As an example we derive the counterterms for the four-point amplitudes. PACS numbers: 11.10.Gh, 11.30.Rd     

First measurements of dtμ cycle characteristics in liquid H/D/T mixture

Muon catalyzed fusion in a dense triple mixture of hydrogen isotopes was investigated for the first time. The experimental method is based on the registration of neutrons from dtμ fusion by a full absorption detector in 4π geometry. The measurements were performed in H/D/T mixture at T=21 K and φ≃ 1.1 LHD using four sets of isotope concentrations. The basic parameters of the dtμ cycle (neutron yield, cycling rate and total sticking) in H/D/T mixtures obtained from neutron time distributions are presented and discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Magnetic order in spin-1 and spin-$$\frac{3} {2}$$ interpolating square-triangle Heisenberg antiferromagnets

We consider coevolution of site state and network structures from different initial substrates: a one dimensional Ising chain, a scale free network and network with non-linear degree dependence. The dynamics is governed by a preassigned stability parameter S, and a rewiring factor φ, that determines whether the Ising spin at the chosen site flips or whether the site gets rewired to another site in the system. We have observed the steady state average stability and magnetisation for both kinds of systems to have an idea about the effect of initial network topology. Although the average stability shows almost similar behaviour, the magnetisation depends on the initial condition we start from. Apart from the local dynamics, the global effect on the dynamics has also been studied. These studies show interesting variations in the steady state values of average stability and magnetisation for different values of S and φ, which helps in indicating the gradual change of existing social networks.     

Distribution of surface states based on Hill and Coleman conductance technique

Hill-Coleman’s single frequency conductance technique for the determination of surface state density has been extended upto 2 kHz. A.c. conductance (G _m) and capacitance (C _m)versus gate bias (V _G) curves were obtained at various signal frequencies. Shift of the observed peaks in theG _m versus V_G curves for different signal frequencies was utilized for the determination of surface state density at different surface potentials (φ _s). Determination of surface state density for differentφ _s values was also done by Nicollian-Goetzberger method and the results compared. Results obtained by Hill-Coleman technique compare reasonably well with those obtained by the other method.     

Search for D+→φl+ν and measurement of the branching fraction for D+→φπ+

Using a data sample of integrated luminosity of about 33 pb^-1 collected around 3.773 GeV with the BESII detector at the BEPC collider, the semileptonic decays D⁺→φe⁺ν_e, D⁺→φμ⁺ν_μ and the hadronic decay D⁺→φπ⁺ are studied. The upper limits of the branching fractions are set to be BF(D⁺→φe⁺ν_e)<2.01% and BF(D⁺→φμ⁺ν_μ)<2.04% at the 90% confidence level. The ratio of the branching fractions for D⁺→φπ⁺ relative to D⁺→K^-π⁺π⁺ is measured to be 0.057±0.011±0.003. In addition, the branching fraction for D⁺→φπ⁺ is obtained to be (5.2±1.0±0.4)×10^-3.     

New critical properties of the Nambu-Jona-Lasinio model with nonzero chemical potential

It is shown for the first time that the massive-fermion state in the Nambu-Jona-Lasinio model with nonzero chemical potential μ is described by two different phases, the transition between which is second-order. It is proved that both first-and second-order phase transitions, depending on the values of the model parameters, restore the chiral symmetry of the model. Two tricritical points exist in the (μ, M) phase diagram (M is the dynamical fermion mass at μ=0). Zh. éksp. Teor. Fiz. 111, 1921–1934 (June 1997)     

Condensation for a Fixed Number of Independent Random Variables

A family of m independent identically distributed random variables indexed by a chemical potential φ∈[0,γ] represents piles of particles. As φ increases to γ, the mean number of particles per site converges to a maximal density ρ _c <∞. The distribution of particles conditioned on the total number of particles equal to n does not depend on φ (canonical ensemble). For fixed m, as n goes to infinity the canonical ensemble measure behave as follows: removing the site with the maximal number of particles, the distribution of particles in the remaining sites converges to the grand canonical measure with density ρ _c ; the remaining particles concentrate (condensate) on a single site.     

Model for laser-induced thermal degradation and ablation of polymers

Ablation of organic polymers is described on the basis of photothermal bond breaking within the bulk material. Here, we assume a first-order chemical reaction, which can be described by an Arrhenius law. Ablation starts when the density of broken bonds at the surface reaches a certain critical value. In order to understand the ablation behavior near the threshold fluence, φ_th, non-stationary regimes must be considered. The present treatment reveals several qualitative differences with respect to models that treat ablation as a surface process: (i) Ablation starts sharply with a front velocity that has its maximum value just after the onset. (ii) The transition to the quasi-stationary ablation regime is faster. (iii) Near threshold, the ablated depth h has a square-root dependence on laser fluence, i.e., h∝(φ-φ_th)^1/2. The ablation velocity is very high even near φ_th. (iv) With φ≈φ_th ablation starts well after the laser pulse. (v) The depletion of species is responsible for the Arrhenius tail observed with fluences φ≤φ_th. (vi) Residual modification of material has maximum near the threshold. (vii) Stationary regimes of ablation demonstrate change of effective activation energy with laser intensity. The model calculations are applied to Polyimide (Kapton^TM H). Here, differences in single-pulse ablated depth determined from mass loss and profilometry should be about 10 nm. Received: 16 February 1999 / Accepted: 18 February 1999 / Published online: 28 April 1999     

Analysis of Bs→φ?+?? decay with new-physics effects

The rare B _s →φ ℓ ⁺ ℓ ⁻decay is investigated by using the most general model-independent effective Hamiltonian for ℓ=μ,τ. The calculated value of Br(B _s →φ μ ⁺ μ ⁻)=1.92×10⁻⁶ is consistent with the experimental upper bound. The dependencies of the branching ratios and polarization asymmetries of leptons and combined lepton–antilepton asymmetries on the new Wilson coefficients are presented. The analysis shows that the branching ratios and the lepton-polarization asymmetries are very sensitive to scalar- and tensor-type interactions. The results obtained in this work will be very useful in searching new physics beyond the standard model.     

Interaction of Muons with H2/H3-Centres in Diamond

We report on transverse field muon spin rotation measurements on a nitrogen-rich type Ia diamond, both before and after the conversion of some of the aggregated nitrogen centres to nitrogen-vacancy complexes known as H2/H3-centres. The prompt fractions f and the spin relaxation rates λ were determined for the diamagnetic (μ_d) and the paramagnetic (Mu_T) states in the temperature range 10–300 K. The production of the nitrogen-vacancy complexes had little effect on the parameters of the Mu_T state for which f and λ remained unchanged at approximately 30% and 4 μs⁻¹, respectively. For the μ_d state, on the other hand, the formation of the H2/H3-centres resulted in an increase of the prompt fraction from 10(2)% to 20(3)%, and (for the first time) the spin relaxation rate showed a non-zero value of 0.020(3) μs⁻¹. These results show evidence of strong μ_d interactions with the nitrogen-vacancy complexes in diamond, and suggest a more complex structure for this state than a bare μ⁺. This revised version was published online in September 2006 with corrections to the Cover Date.     

Josephson effect in superconducting constrictions with hybrid SF electrodes: Peculiar properties determined by the misorientation of magnetizations

Josephson current in SFcFS junctions with arbitrary transparency of the constriction (c) is investigated. The emphasis is on the analysis of the supercurrent dependencies on the misorientation angle θ between the in-plane magnetizations of diffusive ferromagnetic layers (F). It is found that the current-phase relation I(φ) may be radically modified with the θ variation: the harmonic I ₁ sin φ vanishes for a definite value of θ provided that, for an identical orientation of the magnetizations (θ = 0), the junction is in the “π” state. The Josephson current may exhibit a nonmonotonic dependence on the misorientation angle both for realization of the “0” and “π” state at θ = 0. We also analyze the effect of the exchange field induced enhancement of the critical current, which may occur in a definite range of θ. The text was submitted by the author in English.     

Experimental investigation of muon-catalyzed t + t fusion

The muon-catalyzed fusion (μCF) process in tritium was studied by the μCF collaboration on the muon beam of the JINR Phasotron. The measurements were carried out with a liquid tritium target at the temperature 22 K and density approximately 1.25 of the liquid hydrogen density (LHD). Parameters of the μCF cycle were determined: the ttμ muonic molecule formation rate λ _ttμ = 2.84(0.32) μs⁻¹, the ttμ fusion reaction rate λ _f = 15.6(2.0) μs⁻¹, and the probability of muon sticking to helium ω _tt = 13.9(1.5)%. The results agree with those obtained earlier by other groups, but better accuracy was achieved due to our unique experimental method. The article is published in the original.