Thermal shock testing for assuring reliability of glass-sealed microelectronic packages

Tests were performed to determine if thermal shocking is destructive to glass-to-metal seal microelectronic packages and if thermal shock step stressing can compare package reliabilities. Thermal shocking was shown to be not destructive to highly reliable glass seals. Pin-pull tests used to compare the interfacial pin glass strengths showed no differences between thermal shocked and not-thermal shocked headers. A 'critical stress resistance temperature' was not exhibited by the 14 pin Dual In-line Package (DIP) headers evaluated. Headers manufactured in cryogenic nitrogen based and exothermically generated atmospheres showed differences in as-received leak rates, residual oxide depths and pin glass interfacial strengths; these were caused by the different manufacturing methods, in particular, by the chemically etched pins used by one manufacturer. Both header types passed thermal shock tests to temperature differentials of 646 C. The sensitivity of helium leak rate measurements was improved up to 70 percent by baking headers for two hours at 200 C after thermal shocking

Strategies for Mangrove Rehabilitation in an Eroded Coastline of Selangor, Peninsular Malaysia

Continuous mangrove ecosystem degradation and coastal erosion is observed along the coastline of SungaiHaji Dorani, (N 03038'36.6”; E 101000'37.3” to N 03038'37.9”; E 101000'34.0”) Selangor, PeninsularMalaysia. Foreshore mangrove plantation challenges below mean sea level are in progress in this highenergy coast. There are interventions of gabion breakwaters and geo-textile tubes to alleviate the wavevelocity striking the shore. The area between the breakwaters and coastline is chosen for mangroveplantation. The soil is fluid silt sludge with average clay, silt and sand proportion of 43.03 %, 351.8 % and5.14 % respectively. The maximum height of the tide recorded onshore was 2.8 m and in the middle of theplantation area the height of the water flooding is ±3.5 daily during tides. Number of plant species on theSAUH concrete revetment is 43 with 12 mangrove species and on the fringe reference mangroves is 27 with8 true mangrove species. This paper explains the method to identify the potential location for mangroverehabilitation, possibility of establishing mangroves on the seafront in the chosen area and conservation ofthe existing strip with 14 mangrove species. Overall sediment accretion since May 2008 is ±0.0037cm perannum which is considerably negligible. Opening out the earthen bunds along the coastline is the actualsolution for natural mangrove translocation and stabilization in this particular coastline, however, it is notpractically possible. Hence, we have studied an alternative strategy of rehabilitating mangroves at theelevation of +0.5 m to 1m MSL along this shoreline and also in an engineered firm sediment filled zone. Wepropose carrying out hydrological restoration in the natural habitats for survival and further naturalcolonization of mangroves

Depth-Resolved Subsurface Defect Detection in Ceramics Using Optical Gating Techniques

Components made from advanced ceramics materials find widespread use in many industrial and military applications. However, the presence of defects in the bulk and on the surface of the ceramic parts can alter their operation and lead to a reduced lifetime or a catastrophic failure. These defects may include various inclusions, inherent powder defects, poorly distributed second phase material, as well as voids and cracks. They can be introduced at each stage of the manufacturing process. Near-surface defects are particularly critical in many applications since the stresses in this region of the ceramic component are greatest during the operation. These flaws may be intrinsic to the bulk material or can be introduced in the final stages of fabrication (e.g. machining, grinding and polishing). Additionally, in composite ceramics defects can appear as a delamination of internal layers. Because the potential market for ceramic components is so large, a considerable effort has been put into developing non-destructive evaluation (NDE) techniques to detect flaws at various stages of the manufacturing process [1–5]

Exotic spacetimes, superconducting strings with linear momentum, and (not quite) all that

We derive the general exact vacuum metrics associated with a stationary (non static), non rotating, cylindrically symmetric source. An analysis of the geometry described by these vacuum metrics shows that they contain a subfamily of metrics that, although admitting a consistent time orientation, display "exotic" properties, such as "trapping" of geodesics and closed causal curves through every point. The possibility that such spacetimes could be generated by a superconducting string, endowed with a neutral current and momentum, has recently been considered by Thatcher and Morgan. Our results, however, differ from those found by Thatcher and Morgan, and the discrepancy is explained. We also analyze the general possibility of constructing physical sources for the exotic metrics, and find that, under certain restrictions, they must always violate the dominant energy condition (DEC). We illustrate our results by explicitly analyzing the case of concentric shells, where we find that in all cases the external vacuum metric is non exotic if the matter in the shells satisfies the DEC.Comment: 13 pages with no figures. Accepted in PR

Design of robust 2,2′-bipyridine ligand linkers for the stable immobilization of molecular catalysts on silicon(111) surfaces

The attachment of the 2,2′-bipyridine (bpy) moieties to the surface of planar silicon(111) (photo)electrodes was investigated using ab initio simulations performed on a new cluster model for methyl-terminated silicon. Density functional theory (B3LYP) with implicit solvation techniques indicated that adventitious chlorine atoms, when present in the organic linker backbone, led to instability at very negative potentials of the surface-modified electrode. In prior experimental work, chlorine atoms were present as a trace surface impurity due to required surface processing chemistry, and thus could plausibly result in the observed surface instability of the linker. Free energy calculations for the Cl-atom release process with model silyl-linker constructs revealed a modest barrier (14.9 kcal mol⁻¹) that decreased as the electrode potential became more negative. A small library of new bpy-derived structures has additionally been explored computationally to identify strategies that could minimize chlorine-induced linker instability. Structures with fluorine substituents are predicted to be more stable than their chlorine analogues, whereas fully non-halogenated structures are predicted to exhibit the highest stability. The behavior of a hydrogen-evolving molecular catalyst Cp*Rh(bpy) (Cp* = pentamethylcyclopentadienyl) immobilized on a silicon(111) cluster was explored theoretically to evaluate differences between the homogeneous and surface-attached behavior of this species in a tautomerization reaction observed under reductive conditions for catalytic H₂ evolution. The calculated free energy difference between the tautomers is small, hence the results suggest that use of reductively stable linkers can enable robust attachment of catalysts while maintaining chemical behavior on the electrode similar to that exhibited in homogeneous solution

High Aspect Ratio Silicon Wire Array Photoelectrochemical Cells

In an effort to develop low-cost solar energy conversion techniques, high uniformity vertically oriented silicon wire arrays have been fabricated. These arrays, which allow for radial diffusion of minority charge carriers, have been measured in a photoelectrochemical cell. Large photovoltages (∼400 mV) have been measured, and these values are significantly greater than those obtained from the substrate alone. Additionally, the wire array samples displayed much higher current densities than the underlying substrate, demonstrating that significant energy conversion was occurring due to the absorption and charge-carrier transport in the vertically aligned Si wires. This method therefore represents a step toward the use of collection-limited semiconductor materials in a wire array format in macroscopic solar cell devices

Veiled Women in the American Courtroom: Is the Niqab a Barrier to Justice?

U.S. courts and policy-makers have recently authorized laws and practices that interfere with the wearing of religious modesty attire that conceals the hair or face in contexts such as courtroom testimony or driver’s license issuance. For example, in response to a court’s dismissal of the case of a woman who refused to remove her niqab in the courtroom, the Michigan Supreme Court decided that judges can exercise “reasonable control” over the appearance of courtroom parties. But what degree of control over religious attire is reasonable? The Constitution will not allow a blanket niqab removal policy based on any of the following needs: to judge demeanor or veracity, to identify witnesses, to compel accountability, or to identify and avert bias. Where the state’s interest in niqab removal is truly compelling, for the sake of religious free exercise it should be protected in the least restrictive manner. I argue that because Muslim women who wear the niqab in the courtroom are neither disruptive nor an affront to the dignity of the court, their religious freedom to dress modestly should be accommodated in straightforward and available ways

Quantum Theory and Time Asymmetry

The relation between quantum measurement and thermodynamically irreversible processes is investigated. The reduction of the state vector is fundamentally asymmetric in time and shows an observer-relatedness which may explain the double interpretation of the state vector as a representation of physical states as well as of information about them. The concept of relevance being used in all statistical theories of irreversible thermodynamics is shown to be based on the same observer-relatedness. Quantum theories of irreversible processes implicitly use an objectivized process of state vector reduction. The conditions for the reduction are discussed, and I speculate that the final (subjective) observer system might even be carried by a spacetime point.Comment: Latex version of a paper published in 1979 (with minor revisions), 18 page

Quantum Mechanics Calculations of the Thermodynamically Controlled Coverage and Structure of Alkyl Monolayers on Si(111) Surfaces

The heat of formation, ΔE, for silicon (111) surfaces terminated with increasing densities of the alkyl groups CH_3- (methyl), C_2H_5- (ethyl), (CH_3)_2CH- (isopropyl), (CH_3)_3C- (tert-butyl), CH_3(CH_2)_5- (hexyl), CH_3(CH_2)_7- (octyl), and C_6H_5- (phenyl) was calculated using quantum mechanics (QM) methods, with unalkylated sites being H-terminated. The free energy, ΔG, for the formation of both Si−C and Si−H bonds from Si−Cl model componds was also calculated using QM, with four separate Si−H formation mechanisms proposed, to give overall ΔG_S values for the formation of alkylated Si(111) surfaces through a two step chlorination/alkylation method. The data are in good agreement with measurements of the packing densities for alkylated surfaces formed through this technique, for Si−H free energies of formation, ΔG_H, corresponding to a reaction mechanism including the elimination of two H atoms and the formation of a C C double bond in either unreacted alkyl Grignard groups or tetrahydrofuran solvent

Theoretical Investigation of the Structure and Coverage of the Si(111)−OCH_3 Surface

The surface structure, strain energy, and charge profile of the methoxylated Si(111) surface, Si(111)−OCH_3, has been studied using quantum mechanics, and the results are compared to those obtained previously for Si(111)−CH_3 and Si(111)−C_2H_5. The calculations indicate that 100% coverage is feasible for Si(111)−OCH_3 (similar to the methylated surface), as compared to only ∼80% coverage for the ethylated surface. These differences can be understood in terms of nearest-neighbor steric and electrostatic interactions. Enthalpy and free energy calculations indicate that the formation of the Si(111)−OCH_3 surface from Si(111)−H and methanol is favorable at 300 K. The calculations have also indicated the conditions under which stacking faults can emerge on Si(111)−OCH_3, and such conditions are contrasted with the behavior of Si(111)−CH_3 and Si(111)−CH_2CH_3 surfaces, for which stacking faults are calculated to be energetically feasible when etch pits with sufficiently long edges are present on the surface