Resonantly enhanced off-specular X-ray scattering from polymer/polymer interfaces<Superscript>⋆</Superscript>

We have used measurements of the absolute intensity of diffuse X-ray scattering to extract the interfacial tension of a buried polymer/polymer interface. Diffuse scattering was excited by an X-ray standing wave whose phase was adjusted to have a high intensity at the polymer/polymer interface and simultaneously a node at the polymer/air interface. This method permits the capillary-wave-induced roughness of the interface, and hence the interfacial tension, to be measured independently of the polymer/polymer interdiffusion.     

Efficiency of the Incomplete Enumeration Algorithm for Monte-Carlo Simulation of Linear and Branched Polymers

We study the efficiency of the incomplete enumeration algorithm for linear and branched polymers. There is a qualitative difference in the efficiency in these two cases. The average time to generate an independent sample of configuration of polymer with n monomers varies as n ² for linear polymers for large n, but as exp(cn ^α) for branched (undirected and directed) polymers, where 0<α<1. On the binary tree, our numerical studies for n of order 10⁴ gives α = 0.333±0.005. We argue that α =1/3 exactly in this case. An erratum to this article can be found at .     

Fiber Optic Excitation of Silicon Microspheres in Amorphous and Crystalline Fluids

ABSTRACT

This study investigates the optical resonance spectra of free-standing monolithic single crystal silicon microspheres immersed in various amorphous fluids, such as air, water, ethylene glycol, and 4-Cyano-4’-pentylbiphenyl nematic liquid crystal. For the various amorphous fluids, morphology-dependent resonances with quality factors on the order of 10⁵ are observed at 1428 nm. The mode spacing is always on the order of 0.23 nm. The immersion in various amorphous fluids affects the spectral response of the silicon microsphere and heralds this technique for use in novel optofluidics applications. Even though the nematic liquid crystal is a highly birefringent, scattering, and high-index optical medium, morphology-dependent resonances with quality factors on the order of 10⁵ are observed at 1300 nm in the elastic scattering spectra of the silicon microsphere, realizing a liquid-crystal-on-silicon geometry. The relative refractive index and the size parameter of the silicon microsphere are the parameters that affect the resonance structure. The more 4-Cyano-4’-pentylbiphenyl interacting with the silicon microsphere, the lower the quality factor of the resonances is. The more 4-Cyano-4’-pentylbiphenyl is interacting with the silicon microsphere, the lower the mode spacing Δλ of the resonances is. The silicon microspheres wetted with nematic liquid crystal can be used for optically addressed liquid-crystal-on-silicon displays, light valve applications, or reconfigurable optical networks.     

基于DEMON线谱的轴频提取方法研究

目标的螺旋桨不同则轴频不相同。轴频是目标的特征之一,可以应用于目标识别当中。本文提出一种改进的高频噪声解调分析(DEMON)方法,能够得到具有明显线谱的DEMON谱;提出最大公约数算法,并给出提取轴频的具体步骤。海试数据实验结果验证了本文所提方法及算法的有效性和可行性。     

Stabilization of atmospheric carbon dioxide via zero emissions-An alternative way to a stable global environment. Part 1: Examination of the traditional stabilization concept

The concept of "stabilization" of atmospheric CO2 concentration is re-examined in connection with climate-change mitigation strategies. A new "zero-emissions stabilization (Z-stabilization)" is proposed, where CO2 emissions are reduced to zero at some time and thereafter the concentration is decreased by natural removal processes, eventually reaching an equilibrated stable state. Simplified climate experiments show that, under Z-stabilization, considerably larger emissions are permissible in the near future compared with traditional stabilization, with the same constraint on temperature rise. Over longer time scales, the concentration and temperature decrease close to their equilibrium values, much lower than those under traditional stabilization. The smaller temperature rise at final state is essential to avoid longer-term risk of sea level rise, a significant concern under traditional stabilization. Because of these advantages a Z-stabilization pathway can be a candidate of practical mitigation strategies as treated in Part 2.(Contributed by Taroh MATSUNO, M.J.A.).     

Physisorption kinetics of electrons at plasma boundaries

Plasma-boundaries floating in an ionized gas are usually negatively charged. They accumulate electrons more efficiently than ions leading to the formation of a quasi-stationary electron film at the boundaries. We propose to interpret the build-up of surface charges at inert plasma boundaries, where other surface modifications, for instance, implantation of particles and reconstruction or destruction of the surface due to impact of high energy particles can be neglected, as a physisorption process in front of the wall. The electron sticking coefficient s_e and the electron desorption time τ_e, which play an important role in determining the quasi-stationary surface charge, and about which little is empirically and theoretically known, can then be calculated from microscopic models for the electron-wall interaction. Irrespective of the sophistication of the models, the static part of the electron-wall interaction determines the binding energy of the electron, whereas inelastic processes at the wall determine s_e and τ_e. As an illustration, we calculate s_e and τ_e for a metal, using the simplest model in which the static part of the electron-metal interaction is approximated by the classical image potential. Assuming electrons from the plasma to loose (gain) energy at the surface by creating (annihilating) electron-hole pairs in the metal, which is treated as a jellium half-space with an infinitely high workfunction, we obtain s_e≈10^-4 and τ_e≈10^-2 s. The product s_eτ_e≈10^-6 s has the order of magnitude expected from our earlier results for the charge of dust particles in a plasma but individually s_e is unexpectedly small and τ_e is somewhat large. The former is a consequence of the small matrix elements occurring in the simple model while the latter is due to the large binding energy of the electron. More sophisticated theoretical investigations, but also experimental support, are clearly needed because if s_e is indeed as small as our exploratory calculation suggests, it would have severe consequences for the understanding of the formation of surface charges at plasma boundaries. To identify what we believe are key issues of the electronic microphysics at inert plasma boundaries and to inspire other groups to join us on our journey is the purpose of this colloquial presentation.     

Contours of constant Δ and Ψ in the 2–4 plane for the ellipsometric functions

Contour graphs of ₂ vs ₄ for different film thicknesses and a range of angles of incidence have been plotted for the ellipsometric functions Δ and Ψ in both the reflection and transmission modes. In the case of reflection ellipsometry, when the plots for Δ_R and Ψ_R are superimposed, the two sets of contours cross nearly at right angles over a large part of the field, this being indicative of the high accuracy obtainable in using this technique to determine ₄ and ₂ and hence the optical constants, n and k, for the film material. The reflection ellipsometric technique is accurate over angles of incidence between 30° and 75° and for a range of film thicknesses between λ/30 and 5λ. Transmission ellipsometry is less useful, due to anomalies in both X_s and X_p where sudden phase changes of ±π occur in regions of interest. There is also the possibility of multiple solutions, although the use of a multiangle technique would enable the “correct” values to be more easily determined.     

The polynomial reconstruction problem: The first 50 years

The problem of reconstructing the characteristic polynomial of a graph of order at least 3 from the collection of characteristic polynomials of its vertex-deleted subgraphs was posed by Cvetkovi? in 1973 as a spectral counter part to the well-known Ulam's reconstruction conjecture. Over the last 50 years, this problem has received notable attention, many positive results have been obtained, but in the general case the problem is still unresolved. In particular, no counter example is found in literature. In this expository paper we survey classical and some more recent results concerning the polynomial reconstruction problem, discuss some related problems, variations and generalizations.     

Effect of structural relaxation on Curie temperature and magnetostriction investigated by magnetoelastic waves in metglas

Summary Magnetoelastic wave amplitude, a, was measuredvs. the temperature during thermal cycles in Metglas 2826. When the Curie temperature,T _C, has been reached, theA value vanishes due to the fall of the magnetoelastic coupling in the paramagnetic state. This allows evaluation of theT _c temperature. The latter increases after the iterated thermal treatments while the magnetic anisotropyK _u decreases. Also theA amplitude, measured at room temperature after the subsequent thermal treatments, shows an increasing behaviour. The values ofK _u ,T _c andA approach saturation after the same number of thermal cycles; this suggests that the structural relaxation produced by annealing is the microscopic mechanism governing all the three physical quantities. In particular we explain the connection betweenK _u andA by means of the longitudinal magnetostriction.

---

Riassunto L'ampiezza delle onde magnetoelastiche,A, è stata misurata in funzione della temperatura eseguendo cicli termici nel Metglas 2826. Raggiunta la temperatura di Curie,T _C l'ampiezzaA si annulla a causa della transizione dell'accoppiamento magnetoelastico nello stato paramagnetico. Ciò ci mette in grado di misurare la temperaturaT _C; quest'ultima aumenta in seguito ai ripetuti trattamenti termici mentre l'anisotropia magneticaK _u diminuisce. Anche l'ampiezzaA, misurata a temperatura ambiente dopo i trattamenti termici, mostra un andamento crescente. I valori diK _u,T _c eA tendono alla saturazione dopo lo stesso numero di cicli termici; ciò suggerisce che il rilassamento strutturale prodotto dalla ricottura è il meccanismo microscopico che regola le tre grandezze fisiche menzionate. In particolare noi mostriamo cheK _u eA sono legati dalla magnetostrizione longitudinale.

---

Резюме Измеряется зависимость амплитуды магнитноупругой волны,A, от температуры в течение температурных циклов в металлическом стекле 2826. При достижении температуры Кюри,T _c, величинаA обращается в нуль из-за уменьшения магнитноупругой связи в парамагнитном состоянии. Это позволяет оценить темпаратуру Кюри,T _c. Температура Кюри увеличивается после повторных температурных обработок, тогда как магнитная анизотропияK _u уменьшается. Также отмечается увеличение амплитудыA, измеренной при комнатной температуре после последовательных температурных обработок. ВеличиныK _u,T _c иA приближаются к насьщению после одинакового числа температурных циклов. Это результат предполагает, что структурная релаксация, обусловленная отжигом, представляет микроскопический механизм, определяющий все три физические величины. В частности, мы объсняем связь междуK _u иA с помощью продольной магнитострикции.