Reconstruction of composite in-line electron holograms using a small emission cone

We report a new method that gives atomic resolution in the reconstruction of simulated holograms in theoretical low energy electron point source (LEEPS) microscopy, and that uses a screen size that is commensurate with screen sizes used in experimental LEEPS. The method exploits the spherical symmetry in the electron waves emerging from the source. We compare holograms obtained by rotating the screen about an axis passing through the point source as opposed to rotating the atomic cluster in the opposite sense about the same axis. We show that, by generating and combining simulated holograms obtained by rotating the cluster, with the screen held fixed, a composite hologram, comprised of the individual holograms, captures enough information that atomic resolution in the reconstructions is obtained. A key feature is to choose the rotations to optimize the collective interference pattern on the composite hologram. This results in sharper resolution while using a considerably smaller screen size; results are reported for a screen size about ten times smaller than screen sizes typically used in theoretical LEEPS. The method used gives commensurate or better resolution on comparison to results obtained using the larger screen size. Possible implications for experimental LEEPS are briefly discussed.     

Radar target discrimination using the extinction-pulse technique

An aspect independent radar target discrimination scheme based on the natural frequencies of the target is considered. An extinction-pulse waveform upon excitation of a particular conducting target results in the elimination of specified natural modal content of the scattered field. Excitation of a dissimilar target produces a noticeably different late-time response. Construction of appropriate extinction-pulse waveforms is discussed, as well as the effects of random noise on their application to thin cylinder targets. Also presented is experimental verification of this discrimination concept using simplified aircraft models.     

Explicit formulae for the flange efficiency of curved beams

Deformation of the cross-section of a curved beam of thin-walled open section, such as a channel-section formed from thin sheet material, leads to loss of stiffness due to reduced effectiveness of the flanges. Explicit formulae are derived for the flange efficiency of curved beams of channel, Z– and I–section, in which the geometric parameters on which loss of flange efficiency depends are easily identified. The formulae are readily adapted for curved beams of composite material, identifying also the particular properties of the laminate that relate to flange efficiency. The formulae are approximate, but nevertheless of good accuracy in the practical range of designs.     

Frequency domain E-pulse synthesis and target discrimination

A frequency domain approach to theE-pulse radar target discrimination scheme is introduced. This approach is shown to allow easier interpretation ofE-pulse convolutions via theE-pulse spectrum, and leads to a simplified calculation of pulse basis function amplitudes in theE-pulse expansion. Experimental evidence obtained using aircraft models verifies the single-mode discrimination scheme, as well as the aspect-independent nature of theE-pulse technique. This leads to an integrated technique for target discrimination combining theE-pulse with single mode extraction waveforms.     

Topology optimization of periodic layouts of dielectric materials

A topology optimization method is used to design two dimensional periodic structures with desirable transmission properties by distributing two materials of different permittivity over a rectangular representative cell. A plane wave expansion of the electric field at the input and output boundaries is used in the analysis. This allows non-homogeneous material distributions near the boundaries. Numerical examples are used to verify the robustness of the method and to investigate the importance of retaining higher modes in the expansions. It is found that the optimization problem typically admits possibly many local optima and the relevance of higher modes depends on the nature of the solution found. In some instances, higher modes play an important role and using only the dominant mode in the analysis is shown to result in errors in the evaluation of the performance of the design.     

A scaled 0.25-μm bipolar technology using full e-beamlithography

The full leverage offered by electron-beam lithography has been exploited in a scaled 0.25-μm double polysilicon bipolar technology. Devices and circuits were fabricated using e-beam lithography for all mask levels with level-to-level overlays tighter than 0.06 μm. Ion implantation was used to form a sub-100-nm intrinsic base profile, and a novel in-situ doped polysilicon emitter process was used to minimize narrow emitter effects. Transistors with 0.25-μm emitter width have current gains above 80 and cutoff frequencies as high as 40 GHz. A record ECL gate delay of 20.8 ps at 4.82 mW has been measured together with a minimum power-delay product of 47 fJ (42.1 ps at 1.12 mW). These results demonstrate the feasibility and resultant performance leverage of aggressive scaling of conventional bipolar technologies     

Effects of STN DBS on memory guided force control in Parkinson's disease (June 2007).

This study examined the control of elbow force in nine patients with Parkinson's disease when visual feedback was available and when visual feedback was removed to determine how medication (Meds) and unilateral deep brain stimulation (DBS) of the subthalamic nucleus (STN) affect memory guided force control. Patients were examined in each of four treatment conditions: 1) off treatment; 2) Meds; 3) STN DBS; and 4) Meds plus STN DBS. With visual feedback available, there was no difference in force output across treatment conditions. When visual feedback was removed force output drifted under the target in both the off-treatment and the Meds conditions. However, when on STN DBS or Meds plus STN DBS force output drifted above the target. As such, only STN DBS had a significant effect on force output in the vision removed condition. Increased force output when on STN DBS may have occurred due to disruptions in the basal ganglia-thalamo-cortical circuitry. We suggest that modulation of output of the internal segment of the globus pallidus by STN DBS may drive the effect of STN DBS on memory guided force control.     

A Practical Implementation of Silicon Microchannel Coolers for High Power Chips

This paper describes a practical implementation of a single-phase Si microchannel cooler designed for cooling very high power chips such as microprocessors. Through the use of multiple heat exchanger zones and optimized cooler fin designs, a unit thermal resistance 10.5 C-mm² /W from the cooler surface to the inlet water was demonstrated with a fluid pressure drop of <35kPa. Further, cooling of a thermal test chip with a microchannel cooler bonded to it packaged in a single chip module was also demonstrated for a chip power density greater than 300W/cm². Coolers of this design should be able to cool chips with average power densities of 400W/cm² or more     

A comparison between the finite element and frequency response methods in the assessment of thermal striping damage

When incompletely mixed, hot and cold fluid streams pass adjacent to the surface of a component or structure, and cause thermal striping on the surface. The existing methods of assessment of the consequent thermal fatigue damage have been implemented in the computer codes CLOUDBURST, TBL and STRIPE, and these have been shown to be in good agreement. Analysis of temporally random striping is possible in two of the methods, whereas use of the finite element method in such a fatigue analysis may lead to impractically long run times. However, for the special case of sinusoidal patterns of striping, comparison is made in this paper between TBL and the finite element method for the assessment of thermal striping damage.

A fully restrained, single edge cracked plate and a circumferentially cracked cylinder, axially restrained and unrestrained, have been subjected to sinusoidal surface striping for various representative temporal frequencies. The resulting stress intensity factor fluctuations have been determined for various crack depths using the finite element computer code ABAQUS and the analytical code TBL. Good comparisons have been obtained in all cases.