新疆全新世自然环境演变的几个重要时间界线

众多的地质记录表明，全新世新疆环境演变是以暖干为主要特征，但也存在一些次级波动，其演变具有以下几个重要时间界限：１２０００ａＢｐ，９００ａＢＰ，３０００ａＢＰ，１５００ａＢＰ和４００ａＢＰ，全新世期间，新疆地区经历了两种环境演变 影响，故其水热配置格局更为复杂，大致有以下几种类型：暖干，暖湿，冷湿，凉干等。     

Quantum space-times in the year 2002

We review certain emergent notions on the nature of space-time from noncommutative geometry and their radical implications. These ideas of space-time are suggested from developments in fuzzy physics, string theory, and deformation quantization. The review focuses on the ideas coming from fuzzy physics. We find models of quantum space-time like fuzzy S ⁴ on which states cannot be localized, but which fluctuate into other manifolds like CP³. New uncertainty principles concerning such lack of localizability on quantum space-times are formulated. Such investigations show the possibility of formulating and answering questions like the probability of finding a point of a quantum manifold in a state localized on another one. Additional striking possibilities indicated by these developments is the (generic) failure of CPT theorem and the conventional spin-statistics connection. They even suggest that Planck’s ‘constant’ may not be a constant, but an operator which does not commute with all observables. All these novel possibilities arise within the rules of conventional quantum physics, and with no serious input from gravity physics.     

CLIMATE CHANGE AND OPTIMAL ROTATION IN A FLAMMABLE FOREST

ABSTRACT. This paper builds a Faustmann‐based model to study the effects of increased climate‐induced fire risk on the optimal forest rotation period. Simulations using species prevalent in North American forests indicate that both the commercial and socially optimal rotation ages decline as the risk increases. The reduced carbon absorbed by the standing timber can then create a positive feedback effect. This has potentially important policy implications. The Kyoto ratification agreement reached in the autumn of 2001 was dependent on allowing the ‘Umbrella Group’ of countries to use their forests' carbon‐absorbing ability to offset their need for fossil fuel emission reductions. This carbon‐absorbing ability will decline if rotation ages decrease with increased fire risk, weakening the force of the argument for allowing these countries to use their carbon ‘sinks’ to avoid reducing anthropomorphic emissions.     

A harmonized European framework for method validation to support research on emerging pollutants

Any investigation of environmental processes related to chemical substances or their effects depends on reliable, comparable analytical data. This also holds true for the impact of climate change on occurrence, distribution and effects of emerging pollutants, with respect to which there is particular concern regarding the reliability of analytical data, due to lack of harmonization in method validation and requirements for quality assurance and quality control (QA/QC).We present a recent European approach to developing a harmonized framework for method validation, QA/QC and provision of environmental data on emerging pollutants. The validation approach has been tested and improved by three case studies. We outline the main concept of the validation approach as well as the results of the case studies. This European validation framework turned out to be a feasible tool to check the fitness for purpose of analytical methods and to improve the reliability of environmental analytical data, particularly for emerging pollutants.     

Prime number theorems for Rankin-Selberg L-functions over number fields

In this paper we define a Rankin-Selberg L-function attached to automorphic cuspidal represen-tations of GLm(AE) × GLm (AF ) over cyclic algebraic number fields E and F which are invariant under the Galois action,by exploiting a result proved by Arthur and Clozel,and prove a prime number theorem for this L-function.     

An inventory model for slow moving items subject to obsolescence

In this paper, we consider a continuous review inventory system of a slow moving item for which the demand rate drops to a lower level at a known future time instance. The inventory system is controlled according to a one-for-one replenishment policy with a fixed lead time. Adapting to lower demand is achieved by changing the control policy in advance and letting the demand take away the excess stocks. We show that the timing of the control policy change primarily determines the tradeoff between backordering penalties and obsolescence costs. We propose an approximate solution for the optimal time to shift to the new control policy minimizing the expected total cost during the transient period. We find that the advance policy change results in significant cost savings and the approximation yields near optimal expected total costs.     

时间序列中参数变点的检测(英文)

The paper considers the problem of testing for a change point in the parameters of AR（p） models.It is shown that the asymptotically limiting distribution of the residual CUSUM of squares test（RCUSQ） is still the sup of a standard Brownian bridge under null hypothesis.We also show via simulations that our asymptotic results provide good approximations in finite samples.     

Effect of Al doping on the martensitic transition and magnetic entropy change in Ni-Mn-Sn alloys

Effect of Al doping on the martensitic transition and magnetic entropy change in Mn₅₀Ni₄₀Sn_10−xAl_x was investigated. The experimental results show that the martensitic transition temperatures increase with the increase of Al content due to cell contraction, while the martensitic transition temperature range decreases rapidly. Mn₅₀Ni₄₀Sn₈Al₂ alloy has the largest value of  (3.14 J/kg K) for the magnetic field changing from 0 to 10 kOe, which is nearly twice as large as that of Mn₅₀Ni₄₀Sn₁₀ alloy. It is demonstrated that a larger can be obtained due to the sharper magnetization change around martensitic transition.     

Near room temperature magnetocaloric properties of melt-spun Gd100−xBx (x=0, 5, 10, 15, and 20 at%) alloys

The magnetocaloric properties of melt-spun Gd-B alloys were examined with the aim to explore their potential application as magnetic refrigerants near room temperature. A series of Gd_100−xB_x (x=0, 5, 10, 15, and 20 at%) alloys were prepared by melt spinning. With the decrease in Gd/B ratio, Curie temperature (T_C) remains constant at ∼293 K, and saturation magnetization, at 275 K, decreases from ∼100 to ∼78 emu/g. Negligible magnetic hysteresis was observed in these alloys. The peak value of magnetic entropy change, (−ΔS_M)_max, decreased from ∼9.9 J/kg K (0-5 T) and ∼5.5 J/kg K (0-2 T) for melt-spun Gd to ∼7.7 J/kg K (0-5 T) and ∼4.0 J/kg K (0-2 T), respectively for melt-spun Gd₈₅B₁₅ and Gd₈₀B₂₀ alloys. Similarly, the refrigeration capacity (q) decreased monotonously from ∼430 J/kg (0-5 T) for melt-spun Gd to ∼330 J/kg (0-5 T) for melt-spun Gd₈₀B₂₀ alloy. The near room temperature magnetocaloric properties of melt-spun Gd_100−xB_x (0≤x≤20) alloys were found to be comparable to few first-order transition based magnetic refrigerants.     

Effect of position-dependent effective mass on linear and nonlinear optical properties of a cubic quantum dot

In this paper, we first obtain an analytic relation for studying the position-dependent effective mass in a GaAs/Al_xGa_1−xAs cubic quantum dot. Then, the effect of position-dependent effective mass on the intersubband optical absorption coefficient and the refractive index change in the quantum dot are studied. Our numerical calculations are performed using both a constant effective mass and the position-dependent effective mass. We calculate the linear, nonlinear and total intersubband absorption coefficient and refractive index change as a function of the incident optical intensity and structural parameters such as dot length. The results obtained from the present work show that spatially varying electron effective mass plays an important role in the intersubband optical absorption coefficient and refractive index change in a cubic quantum dot.