Thermomagnetic fluctuations and hysteresis loops of magnetic cantilevers for magnetic resonance force microscopy

We have used frequency-shift cantilever magnetometry to study individual nickel magnets patterned at the end of ultra-sensitive silicon cantilevers for use in magnetic resonance force microscopy (MRFM). We present a procedure for inferring a magnet's full hysteresis curve from the response of cantilever resonance frequency versus magnetic field. Hysteresis loops and small-angle fluctuations were determined at 4.2 K with an applied magnetic field up to 6 T for magnets covering a range of dimensions and aspect ratios. Compared to magnetic materials with higher anisotropy, we find that nickel is preferable for MRFM experiments on nuclear spins at high magnetic fields.     

Gcn5p, a transcription-related histone acetyltransferase, acetylates nucleosomes and folded nucleosomal arrays in the absence of other protein subunits

Gcn5p is the catalytic subunit of several type A histone acetyltransferases (HATs). Previous studies performed under a limited range of solution conditions have found that nucleosome core particles and nucleosomal arrays can be acetylated by Gcn5p only when it is complexed with other proteins, e.g. Gcn5-Ada, HAT-A2, and SAGA. Here we demonstrate that when assayed in buffer containing optimum concentrations of either NaCl or MgCl2, purified yeast recombinant Gcn5p (rGcn5p) efficiently acetylates both nucleosome core particles and nucleosomal arrays. Furthermore, under conditions where nucleosomal arrays are extensively folded, rGcn5p acetylates folded arrays approximately 40% faster than nucleosome core particles. Finally, rGcn5p polyacetylates the N termini of free histone H3 but only monoacetylates H3 in nucleosomes and nucleosomal arrays. These results demonstrate both that rGcn5p in and of itself is catalytically active when assayed under optimal solution conditions and that this enzyme prefers folded nucleosomal arrays as a substrate. They further suggest that the structure of the histone H3 N terminus, and concomitantly the accessibility of the H3 acetylation sites, changes upon assembly into nucleosomes and nucleosomal arrays.     

Post-tonsillectomy bacteraemia in children

It has been postulated that the bacteraemia rate following guillotine tonsillectomy is lower than that following dissection tonsillectomy due to intra-operative compression of tonsillar blood vessels by the guillotine. The aim of this study was to evaluate the incidence of bacteraemia following dissection and guillotine tonsillectomy. Sixty-four patients undergoing elective tonsillectomy for recurrent acute tonsillitis were randomly selected, 32 underwent dissection tonsillectomy and 32 guillotine tonsillectomy. Positive intra-operative blood cultures were obtained in 16 patients (25 per cent), nine (28.1 per cent) of the dissection group and seven (21.8 per cent) of the guillotine group. There was no significant difference between the two methods (Chi-squared test, p = 0.77).     

Tool-path planning for rough machining of a cavity by layer-shape analysis

In the manufacture of parts with sculptured cavities from prismatic stock, rough machining usually constitutes most of the machining time owing to the significant difference between the stock and the part shape. When using 2 1/2-D milling or a contour-map approach to do the rough machining, the appropriate selection of tool-path pattern for each cutting layer can significantly reduce rough machining time and hence increase productivity. In this paper, the commonly used toolpath patterns are summarised. A knowledge-based parametric approach for optimising the toolpath pattern of a given cutting layer is proposed. Then, a novel methodology is developed to calculate an arbitrary polygon area and locate the concave cavities in the polygon. Procedures for cutting-layer-shape analysis and the optimal comprehensive tool-path pattern generation are also built and proposed in this paper. These procedures can not only be applied to sculptured cavity parts with simple islands, but also to parts with arbitrarily-shaped islands. Finally, an example is given to illustrate the reasoning process.     

Interconnected metal-ceramic composites by chemical means

Using a sol-gel technique, Ni/α-Al₂O₃ composites with ceramic content ranging from 33–95 vol.% have been synthesized. The process involves dispersing the metal and ceramic precursors in solution followed by calcination in a reducing environment. Fully dense composites are obtained by hot pressing at 1,400°C in an oxygen partial pressure of 10^-12 atm. For the composites containing 20 vol.% metal or higher, the metallic phase was been found to be completely continuous. All of the composites exhibited enhanced fracture toughness behavior relative to the pure ceramic.     

An actively adaptive control for linear systems with random parameters via the dual control approach

A new method is presented for controlling a discrete-time linear system with possibly time-varying random parameters in the presence of input and output noise. The cost is assumed to be quadratic in the state and control. Previous algorithms for the above problem when the system had both zeros and poles unknown were of the open-loop feedback type, i.e., they did not take into account that future observations will be made. Therefore, even though these schemes were adaptive, their learning was "accidental." In contrast to this, the new approach uses an expression of the optimal cost-to-go that exhibits the dual purpose of the control, i.e., learning and control. The effect of the present control on the future estimation ("learning") appears explicitly in the cost used in the stochastic dynamic programming equation. The resulting sequence of controls, which is of the closed-loop type, is shown via simulations to appropriately divide its energy between the learning and the control purposes. Therefore, this control is called actively adaptive because it regulates the speed and amount of learning as required by the performance index. The simulations on a third-order system with six unknown parameters also demonstrate the computational feasibility of the proposed algorithm.     

Finding failures from passed test cases: improving the pattern classification approach to the testing of mesh simplification programs

Mesh simplification programs create three‐dimensional polygonal models similar to an original polygonal model, and yet use fewer polygons. They produce different graphics even though they are based on the same original polygonal model. This results in a test oracle problem. To address the problem, our previous work has developed a technique that uses a reference model of the program under test to train a classifier. Using such an approach may mistakenly mark a failure‐causing test case as passed. It lowers the testing effectiveness of revealing failures. This paper suggests piping the test cases marked as passed by a statistical pattern classification module to an analytical metamorphic testing (MT) module. We evaluate our approach empirically using three subject programs with over 2700 program mutants. The result shows that, using a resembling reference model to train a classifier, the integrated approach can significantly improve the failure detection effectiveness of the pattern classification approach. We also explain how MT in our design trades specificity for sensitivity. Copyright © 2009 John Wiley & Sons, Ltd.     

A Tree-Based Data Collecting Network Structure for Wireless Sensor Networks

In a sensor network with a large number of densely populated sensor nodes, a single target of interest may be detected by multiple sensor nodes simultaneously. Data collected from the sensor nodes are usually highly correlated, and hence energy saving using in-network data fusion becomes possible. A traditional data fusion scheme starts with dividing the network into clusters, followed by electing a sensor node as cluster head in each cluster. A cluster head is responsible for collecting data from all its cluster members, performing data fusion on these data and transmitting the fused data to the base station. Assuming that a sensor node is only capable of handling a single node-to-node transmission at a time and each transmission takes T time-slots, a cluster head with n cluster members will take at least nT time-slots to collect data from all its cluster members. In this paper, a tree-based network structure and its formation algorithms are proposed. Simulation results show that the proposed network structure can greatly reduce the delay in data collection.     

All-Fiber Q-Switched Erbium-Doped Fiber Ring Laser Using Phase-Shifted Fiber Bragg Grating

We propose a unique all-fiber Q-switched erbium-doped fiber ring laser. It consists of a phase-shifted fiber Bragg grating (FBG) and an apodized FBG reflector. By using the piezoelectric transducer (PZT) to periodically stretch the apodized FBG and detune it with the phases-shifted FBG, the cavity loss of the fiber ring laser is switched between high and low states to achieve Q-switching. This Q-switched fiber laser has advantages of narrow spectral bandwidth, stable oscillation wavelength, and the repetition rate of the Q-switched pulses can be double of the PZT modulation frequency. A numerical model is developed and presented to simulate and analyze this FBGs-based Q-switched fiber ring laser with consideration of the dynamic response of FBGs during Q-switching. We experimentally demonstrate 10 and 20 kHz Q-switching operation with 10 kHz PZT modulation frequency. The experimental result is similar to the simulation result.