Silicon Vibrating Wires at Low Temperatures

Nowadays microfabrication techniques originating from micro-electro nics enable to create mechanical objects of micron-size. The field of Micro-Electro-Mechanical devices (MEMs) is continuously expanding, with an amazingly broad range of applications at room temperature. Vibrating objects (torsional oscillators, vibrating wires) widely used at low temperatures to study quantum fluids, can be replaced advantageously by Silicon MEMs. In this letter we report on the study of Silicon vibrating wire devices. A goal-post structure covered with a metal layer is driven at resonance by the Laplace force acting on a current in a magnetic field, while the induced voltage arising from the cut magnetic flux allows to detect the motion. The characteristics of the resonance have been studied from 10 mK to 30 K, in vacuum and in ⁴He gas. In this article, we focus on the results obtained above 1.5 K, in vacuum and gas, and introduce some features observed at lower temperatures. The resonant properties can be quantitatively understood by means of simple models, from the linear regime to a highly non-linear response at strong drives. We demonstrate that the non-linearity is mostly due to the geometry of the vibrators. We also show that in our device the friction mechanisms originate in the metallic layers, and can be fully characterized. The interaction with ⁴He gas is fit to theory without adjustable parameters.      

Molecular structure and interaction of biopolymers as viewed by Fourier transform infrared spectroscopy: model studies on β-lactoglobulin

Fourier transform absorption infrared spectroscopy is a powerful and versatile tool used to determine the molecular structure of biomolecules. This technique is now widely used in biochemistry to study the conformation of biopolymers in aqueous solutions and complex systems. However, its enormous potential in the study of food biopolymers has yet to be reached. The aim of this paper is principally to provide information on biopolymers using Fourier transform infrared spectroscopy. β-Lactoglobulin (β-Lg), the major whey protein in the milk of ruminants, is chosen as a model. Emphasis will be put on the different structure levels of proteins in an aqueous solution, the protein–protein interactions, and the protein interactions with small host-molecules such as phospholipids.     

Temperature Modulation Measurements of the Thermal Properties of Nanosystems at Low Temperatures

We report on the dynamic measurements of thermal properties of nanosystems at very low temperatures. These techniques are based on the modulation of the temperature and hence leads to highly sensitive measurements. We will discuss the intrinsic limitations of these methods when the thermal properties of nano-objects are studied at very low temperatures, much below 1 K. Firstly, we will present thermal conductance measurements using the 3ω method. This technique is limited at low temperatures due to the significant increase of the mean free path. Secondly, heat capacity measurements using ac calorimetry are outlined, and again restrictions occur due to the continuous temperature gradient inherent to that technique. Propositions are made in order to overcome these limitations.     

Retention of Free Liquids in Landfills Undergoing Vertical Expansion

This paper presents the results of an evaluation of the potential release of liquids stored within a waste mass undergoing compression due to a landfill vertical expansion. The mechanism of free liquid generation is initially evaluated and data interpretation methods are developed to estimate the maximum allowable waste thickness that a landfill could reach without releasing liquids stored within the waste. The proposed conceptual framework of free liquid generation is used to evaluate the environmental implications of the vertical expansion of an unlined case history landfill located in southern California. The moisture content of waste in southern California landfills is generally below field capacity. However, if the waste is compressed, its available moisture-holding capacity will decrease and its moisture content may eventually reach field capacity. Additional compression beyond this point will squeeze liquid from the waste. Laboratory testing and field characterization programs were undertaken to evaluate the field capacity, the in-situ moisture distribution, and the unit weight profiles of the waste in the case history landfill. These experimental data were used to evaluate the ability of the landfill to continue to retain moisture after continued waste placement. The evaluation indicated that the moisture content of the waste will not reach its field capacity for the proposed final grading of the case history landfill and, therefore, that the liquids should remain within the waste mass after the vertical expansion.     

The structure of cyclin H: common mode of kinase activation and specific features

The crystal structure of human cyclin H refined at 2.6 A resolution is compared with that of cyclin A. The core of the molecule consists of two repeats containing five helices each and forming the canonical cyclin fold also observed in TFIIB. One hundred and thirty-two out of the 217 C alpha atoms from the cyclin fold can be superposed with a root-mean-square difference of 1.8 A. The structural homology is even higher for the residues at the interface with the kinase, which is of functional significance, as shown by our observation that cyclin H binds to cyclin-dependent kinase 2 (cdk2) and that cyclin A is able to activate cdk7 in the presence of MAT1. Based on this superposition, a new signature sequence for cyclins was found. The specificity of the cyclin H molecule is provided mainly by two long helices which extend the cyclin fold at its N- and C-termini and pack together against the first repeat on the side opposite to the kinase. Deletion mutants show that the terminal helices are required for a functionally active cyclin H.     

Finite-range topical functions and uniformly topical functions

We introduce a remarkable subclass of the class of topical functions, the class of uniformly topical functions, whose dynamical behaviour is investigated. Every uniformly topical endofunction has a spectral vector, related to some special fixed points (possibly at infinity), about which we establish various properties. In the stochastic case, we prove a multiplicative ergodic theorem, asserting that the stochastic spectral vector exists in all cases.     

Comparison of ATM switching architectures

Clear examination of work currently done within CCITT indicates the importance of a broadband telecommunication network. As this network should be capable of integrating all services in an efficient way—in order to reduce cost—the asynchronous transfer mode (ATM) was selected by CCITT as the target transfer mode for implementing the broadband integrated services digital network (BISDN). This selection implies that the switching nodes in the BISDN network are capable of supporting this high-speed packet and connection-orientated technique. Within the literature different switching node architectures based upon ATM have been proposed. All of these architectures should meet the high-speed and high-throughput requirements so as to cope with the delay and jitter performance objectives. In a first step this paper describes alternative switching techniques for the basic building block (switching element) of a switching node. A common model architecture of the switching element is drafted. A classification of switching elements described in the literature is derived and the influence on the complexity and performance is weighted. In a second step the switching node architecture is further elaborated according to the control and flexibility requirements. Core (switching) and edge (switching related) functions are listed, and possible functional partitionings are discussed. Finally, these ATM switching architectures are compared according to a background frame consisting of several straightforward comparison points such as the buffering strategy, the internal routeing method, the switching overhead, the connection-orientated or connectionless operation, etc.     

A study of assessors'' performance using graphical methods

The performance of a sensory panel is studied through analysis of variance and in particular the assessors × products interaction. A graphic can illustrate the partitioning of the interaction by a sum of distances between the assessors. The decomposition of the sum of the product effect plus the interaction allows a vector representation of the assessors. These vectors are classified with an original method in order to point out homogeneous sub-panels. The new classification allows aggregation of groups only when all the correlations between assessors are greater than a threshold.