An infrared heat source for temperature control of a smallmicroscope flow bath

A simple, inexpensive, and easily installed infrared heat source with temperature controller for small superfusion baths used in electrophysiologic experiments is described. The output of a thermal sensor in the bath is amplified and sent to a feedback circuit which in turn controls the voltage supplied to a tungsten/halogen bulb focused on the bath. Fluctuation from the set point is no more than 0.2 degrees C with good fluid level control. Judging from the lack of change in the cardiac action potential duration, heart cells do not preferentially absorb infrared radiation.     

Niagara Cantilever

The first modern metal cantilever bridge in the United States, using erection methods that were to be utilized in most future cantilever bridges, was by C. C. Schneider across the Niagara Gorge in 1883. The Niagara, saw in order, John Roebling’s Railroad Suspension Bridge, Samuel Keefer’s Honeymoon Suspension Bridge, Edward Serrell’s Lewiston-Queenston Suspension Bridge, Schneider’s cantilever, Leffert Buck’s arch bridge at the falls as well as Buck’s arch built under Roebling’s suspension bridge. Schneider’s bridge had a useful life of over 40 years during a period when rolling stock on the railroads was increasing rapidly. The speed of erection of a new style bridge coupled with its performance makes it one of the most innovative and significant bridges built in the world at the time.     

Analysis of Surface Tension from Aerodynamic Levitation of Liquids

Aerodynamic levitation allows contactless diagnostics of very high-temperature liquid properties. Liquids can be metals or inorganic compounds, and the levitation gas may have any composition. Temperature limitation is dependent on the heating power and radiative properties of the samples, with 3000°C possible for oxides. Surface-tension measurement is based on previous theories, which relate it to specific vibrations of the drop. Rotation and precession of liquid drops are specific aspects of aerodynamic levitation, and their effects are quantified here. Experimental examples for nickel and alumina are also shown and compared with results from previous experiments, when available.     

Thermal and thermomechanical effects in dry sliding

Whenever friction occurs in dry sliding of mechanical components, mechanical energy is transformed into heat through surface and volumetric processes in and around the real area of contact. This frictional heating, and the thermal and thermomechanical phenomena associated with it, can have a very important influence on the tribological behavior of the sliding components, especially at high sliding velocities. Significant developments in the study of these phenomena are reviewed in this paper. Among the topics reviewed are mechanisms of frictional heating and the distribution of heat during sliding friction, the measurement and analysis of surface and nearsurface temperatures resulting from frictional heating, thermal deformation around sliding contacts and the changes in contact geometry caused by thermal deformation and thermoelastic instability, and the thermomechanical stress distribution around the frictionally heated and thermally deformed contact spots. The paper concludes with a discussion of the influence of the thermal and thermomechanical contact phenomena on wear, thermocracking and other modes of failure of sliding mechanical components.     

Dislocation substructure inin situ deformed foils of niobium-8 to 10 at % vanadium alloy

The development of dislocation substructure in foils of niobium-8 to 10 at % vanadium alloy deformedin situ in the tensile stage of the microscope is presented to substantiate earlier observations presented in Part 1. The results of direct observation of the formation of straight dislocations, dislocation loops and loop debris are presented. In addition, the behaviour of cracks in foils containing hydrogen is compared with that observed in the absence of the interstitial. Through thein situ observations, the mechanism of embrittlement of niobium-rich vanadium alloys in the presence of hydrogen presented in Part 1 is substantiated.     

Structural studies of fibrinolysis by electron microscopy

Fibrin is degraded by the fibrinolytic system in which a plasminogen activator converts plasminogen to plasmin, a serine protease that cleaves specific bonds in fibrin leading to solubilization. To elucidate further the biophysical processes involved in conversion of insoluble fibers to soluble fragments, fibrin was treated with either plasmin or the combination of plasminogen and plasminogen activator, and morphologic changes were observed using scanning electron microscopy. These changes were correlated with biochemical analysis and with characterization of released, soluble fragments by transmission electron microscopy. Initial changes in the fibrin matrix included creation of many free fiber ends and gaps in the continuity of fibers. With more extensive digestion, free fiber segments associated laterally, resulting in formation of thick fiber bundles. Supernatants of digesting clots, containing soluble derivatives, were negatively contrasted and examined by transmission electron microscopy. Large, complex fragments containing portions of multiple fibers were observed, as were pieces of individual fibers and smaller fragments previously identified. Some large fragments had sharply defined ends, indicating that they had been cleaved perpendicularly to the fiber direction. Other fibers showed splayed ends or a lacy meshwork of surrounding protofibrils. Longer times generated more small fragments whose molecular composition could be inferred from their appearance. These results indicate that fibrinolytic degradation results in larger pieces than previously identified and that plasmin digestion proceeds locally by transverse cutting across fibers rather than by progressive cleavage uniformly around the fiber.     

A self-consistent approximation for crack bridging by elastic/perfectly plastic ligaments

In several contexts where the effectiveness of crack-bridging reinforcements degrades when the static or cyclic stress transmitted by the reinforcements exceeds a threshold value, the reinforcements can be idealized as elastic/perfectly plastic springs with the yield stress corresponding to the threshold stress for degradation. A self-consistent procedure is proposed for estimating the net crack tip stress intensity factor k_tip for a given applied stress, crack length and length of unbridged zone. Plausible analytical representations are postulated for the crack profile over the intervals where the crack-bridging springs respond elastically. The representations involve k_tip as a scaling factor, and lead to implicit formulae for k_tip. When the applied stress exceeds the threshold for degradation, further simplifications yield explicit formulae for k_tip. The best results obtained from these formulae agree closely over much of the parameter space with those obtained more laboriously by solving a non-linear integral equation.

The approximations can be used to assess the influence of cyclic debonding on the effectiveness of externally bonded repairs, or of fiber reinforcement in metal laminates and metal-matrix composites. One of the approximations is an upper bound for k_tip and can therefore offer conservative estimates for the effectiveness of the bonded repair or fiber reinforcement.     

Sequence comparison of the ARG4 chromosomal regions from the two related yeasts,Saccharomyces cerevisiae and Saccharomyces douglasii

A 3·6 kb DNA fragment from Saccharomyces douglasii, containing the ARG4 gene, has been cloned, sequenced and compared to the corresponding region from Saccharomyces cerevisiae. The organization of this region is identical in both yeasts. It contains besides the ARG4 gene, another complete open reading frame (ORF) (YSD83) and a third incomplete one (DED81). The ARG4 and the YSD83 coding regions differ from their S. cerevisiae homologs by 8.1% and 12·5%, respectively, of base substitutions. The encoded proteins have evolved differently: amino acid replacements are significantly less frequent in Arg4 (2·8%) than in Ysc83 (12·4%) and most of the changes in Arg4 are conservative, which is not the case for Ysc83. The non-coding regions are less conserved, with small AT-rich insertions/deletions and 20% base substitutions. However, the level of divergence is smaller in the aligned sequences of these regions than in silent sites of the ORFs, probably revealing a higher degree of constraints. The Gcn4 binding site and the region where meiotic double-strand breaks occur, are fully conserved. The data confirm that these two yeasts are evolutionarily closely related and that comparisons of their sequences might reveal conserved protein and DNA domains not expected to be found in sequence comparisons between more diverged organisms.     

FINDING PLACEMENT SEQUENCES AND BIN LOCATIONS FOR CARTESIAN ROBOTS

We model the repetitive placement by a Cartesian robot of n parts on a rectangular workpiece. There are n bins or feeders (one per part), to be placed around the boundary of the workpiece, which contain the parts. The robot picks a part from a bin, places it, picks another part, places it, etc.; any placement sequence is possible. The problem, to find bin locations and a placement sequence to minimize total assembly time, is formulated as a traveling salesman problem (on a graph with n nodes) with special structure. This structure allows the computation of a lower bound on the minimum total assembly time in order n effort. The lower bound improves as n increases, and leads to a simple solution algorithm which gives asymptotically optimal solutions in order n log n effort. For die case where parts are uniformly distributed on the workpiece, we give simple closed-form expressions for the expected value of the lower bound. These expressions should be helpful for design decisions; for example, holding n constant, they indicate that square workpieces require more assembly time than non-square, rectangular workpieces of the same area. Most of our results are relatively insensitive to the inclusion of robot acceleration/deceleration effects.