Showing papers by "Rensselaer Polytechnic Institute published in 1980"

On the Formation and Occurrence of Saddle Dolomite

Abstract: Saddle dolomite is a variety of dolomite that has a warped crystal lattice; it is characterized by curved crystal faces and cleavage, and sweeping extinction. Perfect saddle forms have trigonal symmetry, with crystal elongation at high angles to the 'c' axis. Saddle dolomite occurs as both a void-filling cement and a replacement mineral and is commonly associated with hydrocarbons, epigenetic base-metal mineralization, and sulfate-rich carbonates. These associations imply late diagenetic formation by sulfate reduction processes. Saddle dolomite is slightly enriched in calcium and has significant variations in composition within individual growth laminae. Calcium is more abundant in the lattice at crystal apices and face edges that are at high angles to the 'c' axis, than towards face centers. These composition gradients along growth laminae cause the lattice distortion which has trigonal symmetry corresponding to the saddle morphology. The cause of selective ion adsorption during crystal growth is open to speculation but must be associated with the crystal as an entity. Surface-charge effects, the most probable cause, may be produced by either a pyro-electric phenomenon at elevated temperatures or pH and ionic concentrations of the precipitating fluids. Saddle dolomite has potential as a geothermometer, being indicative of elevated temperatures (60-150°C).

Anisotropy of Young's modulus of bone

Abstract: Bonfield and Grynpas1 have compared their experimental data for Young's modulus of elasticity versus the angle of orientation of the specimen to the long axis of bone with a theoretical curve predicted from a calculation for fibre reinforced materials proposed by Currey2. As a result of the poor agreement between the two curves they conclude “… an alternative model is required to account for the dependence of Young's modulus on orientation” (ref. 1). Such an alternative has been under development in my laboratory for the past 8 years (refs 3–7). It is a two-level hierarchical fibre-reinforced composite model which appears to provide a much more suitable description of the behaviour of bone as a fibre-reinforced composite material.

An Experimental Study of Endwall and Airfoil Surface Heat Transfer in a Large Scale Turbine Blade Cascade

Abstract: Local rates of heat transfer on the endwall, suction, and pressure surfaces of a large scale turbine blade cascade were measured for two inlet boundary layer thicknesses and for a Reynolds number typical of gas turbine engine operation. The accuracy and spatial resolution of the measurements were sufficient to reveal local variations of heat transfer associated with distinct flow regimes and with regions of strong three-dimensional flow. Pertinent results of surface flow visualization and pressure measurements are included. The dominant role of the passage vortex, which develops from the singular separation of the inlet boundary layer, in determining heat transfer at the endwall and at certain regions of the airfoil surface is illustrated. Heat transfer on the passage surfaces is discussed and measurements at airfoil midspan are compared with current finite difference prediction methods.

Modification of Polymers

Abstract: Polymers of natural origin (gums, fibers, skins) have been used by man since prehistoric times. The technology of improving the useful qualities of such materials was developed empirically without benefit of the unifying conceptual framework of chemistry. The early chemical efforts which lead to the modification of rubber via isomerization with acid (1781)2 or Vulcanization with sulfur (1839)3 were also largely serendipitous discoveries. By the mid-19th century investigators like Bracconnot (1833)4 and Schonbein (1845)5 had begun systematic efforts to apply the emerging science of organic chemistry to the task of modifying the end-use properties of natural materials, or imparting wholly new properties to them. The careful study of the reaction of cellulose with nitric acid ultimately led to Parkes’ production of the first semisynthetic commercial plastic, “Parkesine” (1864)6. The chemistry of polyisoprene isolated from a variety of natural sources was also a subject of intense chemical investigation. It had been chlorinated in 18597, and was later hydrochlorinated in 18818. Weber (1894)9 recognized similarities between the Vulcanization process and the insolubilization of rubber by S2Cl2. The production of rayon by treatment of alkali-cellulose with CS2 was patented in 189210.

Generating all maximal efficient faces for multiple objective linear programs

Abstract: A method for generating the entire efficient set for a multiple objective linear program is developed. The method is based on two characterizations of maximal efficient faces. The first characterization is used to determine the set of maximal efficient faces incident to a given efficient vertex, and the second characterization ensures that previously generated maximal efficient faces are easily recognized (and not regenerated). The efficient set is described as the union of maximal efficient faces. An alternate implicit description of the efficient set as the set of all optimal vectors for a finite set of linear programs is also provided.

Combined source-channel coding of images using the block cosine transform.

Abstract: An approach is described for exploiting the tradeoffs between source and channel coding in the context of image transmission. The source encoder employs two-dimensional (2-D) block transform coding using the discrete cosine transform (DCT). This technique has proven to be an efficient and readily implementable source coding technique in the absence of channel errors. In the presence of channel errors, however, the performance degrades rapidly, requiring some form of error-control protection if high quality image reconstruction is to be achieved. This channel coding can be extremely wasteful of channel bandwidth if not applied judiciously. The approach described here provides a rationale for combined source-channel coding which provides improved quality image reconstruction without sacrificing transmission bandwidth. This approach is shown to result in a relatively robust design which is reasonably insensitive to channel errors and yet provides performance approaching theoretical performance limits. Analytical results are provided for assumed 2-D autoregressive image models, while simulation results are provided for real-world images.

Application of RF Circuit Design Principles to Distributed Power Converters

Abstract: The application of RF circuit design principles to high-frequency power converters is described. Compared to conventional converter design, emphasis is placed on obtaining sinusoidal-type waveforms (instead of rectangular-type waveforms) to minimize device switching time requirements and alleviate transforming requirements. A 25-W 48-V to 5-V dc-to-dc converter design using a 5-MHz switching frequency is presented illustrating these principles, using a Class E power amplifier, an L section impedance transformer, and a shunt-mounted harmonically tuned rectifier circuit. Computer simulation results are presented that indicate the feasibility of the proposed design approach, specify required circuit parameters and indicate that line and load regulation can be achieved with narrow-band frequency control. Experimental results on a low power 5-W, 25-V to 5-V dc-to-dc converter breadboard using a 10-MHz switching frequency with the described circuit topology are presented. An efficiency of 68 percent was obtained and load regulation by frequency control demonstrated. Inductor Q requirements limit the conversion efficiency of the proposed converter, and will probably be the limiting factor in obtaining high efficiency with similar design approaches.

An Analysis of a Real-Time Transform Domain Filtering Digital Communication System--Part I: Narrow-Band Interference Rejection

Abstract: This paper provides a detailed analysis of the performance of systems recently proposed by various authors in which the received signal is Fourier transformed in real time (usually with a surface acoustic wave device) and then filtered by a multiplication of the transformed signal by an appropriate transfer function. We shall refer to this operation as transform domain filtering. General expressions for the output waveforms of the system will be derived, and a specific example illustrating the performance of the system when operating in the presence of a narrow-band interferer plus additive white Gaussian noise will be presented. It will be shown that certain filtering techniques not feasible in conventional systems, such as filtering with ideal bandpass filters, become straightforward using transform domain filtering. Finally, a receiver will be described which will eliminate that intersymbol interference between adjacent data symbols due to filtering at the receiver.

An experimental study of uniaxial creep, cyclic creep and relaxation of aisi type 304 stainless steel at room temperature

Abstract: Following previous work ( Krempl , 1979), a servocontrolled testing machine and strain measurement at the gage length were used to study the uniaxial rate(time)-dependent behavior of AISI Type 304 stainless steel at room temperature. The test results show that the creep strain accumulated in a given period of time depends strongly on the stress-rate preceding the creep test. In constant stress-rate zero-to-tension loading the creep strain accumulated in a fixed time-period at a given stress level is always higher during loading than during unloading. Continued cycling causes an exhaustion of creep ratchetting which depends on the stress-rate. Periods of creep and relaxation introduced during completely reversed plastic cycling show that the curved portions of the hysteresis loop exhibit most of the inelasticity. In the straight portions, creep and relaxation are small and there exists a region commencing after unloading where the behavior is similar to that at the origin for virgin materials. This region does not extend to zero stress. The results are at variance with creep theory and with viscoplasticity theories which assume that the yield surface expands with the stress. They support the theory of viscoplasticity based on total strain and overstress.

Dielectric Properties of Fluid-Saturated Bone

Abstract: The dielectric relaxation of bovine femoral compact bone specimens in vitro, saturated with 0.9 percent NaCI solution is determined by applying a constant current pulse and measuring the change in voltage with time. For specimens in which the current is in the plane perpendicular to the length of the whole bone and along the radial direction (radial specimens), the relaxation is confined to the time domain, t50 ?s; for longitudinal specimens, the relaxation, if any, would be for t1 ?s. The long-time resistivity of the latter is ?45 to 48 ?m; for the radial specimens, it is ?3 to 4 times greater. The resistivity of the fluid is 0.72 ?m. The results indicate that the dielectric behavior of fluid-saturated compact bone in vitro, and, hence, possibly also of in vivo bone, is determined mostly by the fluid-fllled pores. This has implications that contradict some of the commonly accepted views on the electromechanical effect in bone.

Dense hydroxylapatite: fatigue and fracture strength after various treatments, from diametral tests

Abstract: Dense hydroxylapatite was examined with the diametral test at different loading rates, after treatment in different solutions, and under static load. The fatigue tests showed that hydroxylapatite is quite resistant to fatigue as compared with other oxides. The simple Weibull distribution of strengths was not obeyed. Different solution treatments and implanting the hydroxylapatite did not appreciably change its strength.

Correlation effects on alkali ion diffusion in binary alkali oxide glasses

Abstract: The correlation factor in the Nernst-Einstei equation for low sodium Na2OGeO2 glass determined from dc conductivity and 22Na diffusion coefficient measurements was found to be near unity. Values of the correlation factor were also compiled from the literature for higher alkali content germanate glasses as well as for sodium borate and alkali silicate glasses. In all three systems the correlation factor was found to depend primarily on the alkali content in the glass. Specifically, uncorrelated ionic diffusion ( ƒ ⋍ 1 ) occurs in low alkali glasses while correlated motion ( ƒ ) takes place at higher alkali concentrations. This observation is consistent with the theory that many “holes” exist in low alkali glasses through which the diffusing cation can randomly jump.

Phase transitions in mesophase macromolecules. I. Novel behavior in the vitrification of poly(ethylene terephthalate‐co‐p‐oxybenzoate)

Abstract: A 40:60 mole ratio poly(ethylene terephthalate-co-p-oxybenzoate) was studied by dynamic scanning calorimetry. Vitrification occurred in two steps, which could be linked by optical microscopy to a two-phase structure. For the lower glass transition, hysteresis was absent on heating and cooling through the transition temperature. Since all prior studied glasses show such hysteresis, this may be linked to the mesophase structure and raises the question whether mesophases always display such glass-transition behavior.

Maintenance of GI function after bowel surgery and immediate enteral full nutrition. I. Doubling of canine colorectal anastomotic bursting pressure and intestinal wound mature collagen content.

Abstract: Following either standardized stapled resection of an ileal blind loop terminus (17 beagles) or construction of a colorectal anastomosis (10 beagles), half the subjects immediately were fed an elemental diet (Vivonex HN). Gastrointestinal (GI) motility and absorption were maintained by exclusion of swallowed air. Controls received the same rate of feeding solution containing only the electrolyte components. Four days postoperatively, the fed beagle's colorectal anastomosis had over double the bursting pressure of the control, 303 +/- 46 mm Hg (p less than 0.001). At this time, the mature collagen content of the fed subjects' ileal wound was undiminished from that of normal ileum 2,223 +/- 336 versus 2,250 +/- 577, contrasting with the 45% decrease of this structural component (OHP) in the wounds of the unfed controls, 1,237 +/- 820 microgram/g of tissue (p less than 0.001). Similarly, the wounds of fed but not unfed subjects had a doubling (p less than 0.001) in concentration of collagen precursors and "new" collagen. The "catabolic" and "lag" phases, as noted in unfed experimental animals, appeared to be reflections of the relative starvation that accompanied the intestinal wounding. With maintenance of GI function and immediate full enteral nutrition, "accelerated healing" was noted relative to the previously considered "norm".

Naloxone reduces fluid intake: effects of water and food deprivation.

Abstract: Food and fluid deprived and nondeprived male rats showed 36% and 46% decreases, respectively, in sucrose consumption 15-min after injection with 2 mg/kg of naloxone in one hr tests. The magnitude of this decrease was not correlated with an index of naloxone's ability to produce a sickness, as measured by the conditioned taste aversion test. Tests with animals scheduled to drink water in a 15-min daily session showed naloxone had similar effects in reducing water intake in 23-hr and 47-hr water deprived rats. Morphine, when self-administered, produced an increase in water intake during 6-hr sessions. The data support the idea that naloxone disrupts a component of normal regulation of ingestion.

Viral pathogenesis and resistance to defective interfering particles

Abstract: Recently presented evidence indicates that synthesis of defective interfering (DI) particles following infection of cultured cells with lymphocytic choriomeningitis (LCM) virus may result in self-curing1. The genesis of DI particles can occur in cells infected with virtually any animal virus2, and seems to be a host-controlled function3. Thus, these particles may represent a third line of defence—with the immune response and interferon—against virus invasion3,4. LCM virus infection causes the rapid appearance of DI particles in tissue culture cells5,6. Nevertheless, persistent infections can be easily established with LCM and other arenaviruses7–9. The LCM-persistent infections are apparently maintained in these cultures by the genesis of DI-resistant viruses1. This latter finding prompted us to determine whether such DI-resistant viruses occur in nature. Vertical transmission of LCM virus in the house mouse or neonatal infection of laboratory mice takes the form of a life-long inap-parent infection. These mice lack functional virus-specific T lymphocytes, but may make an antibody response against the invasion. It is known that LCM virus injected into a neonatal mouse can change during the course of the infection so that at least two different viral populations coexist in the same mouse10. DI particles are produced in abundance shortly after neonatal infection and this precedes the appearance of a virus population that, by plaque morphology, differs from the one originally inoculated11. We report here the isolation of an LCM virus from persistently infected mice that is resistant not only to the DI particles which were produced shortly after neonatal infection with heterotypic virus but also to the DI particles that this virus itself induces in neonates. We know of no other report of viruses which can replicate normally in the presence of the DI particles they induce.

The effect of fretting and environment on fatigue crack initiation and early propagation in a quenched and tempered 4130 Steel

Abstract: Fretting fatigue studies were performed on quenched and tempered 4130 steel in laboratory air and in argon as functions of relative slip displacement, normal pressure and applied cyclic stress. Significant reductions in fatigue resistance were observed at all stress levels and increased with increasing normal pressures. However, a minimum in resistance was observed for relative slip magnitudes of 20 to 30 μm. Inert environments improve fatigue resistance under fretting conditions. Metallographic observations indicated that subsurface cracking was generally observed and that stress concentrations associated with this cracking resulted in deviations to and away from the faying surfaces. Fretting cracks which deviated into the alloy become initiated fatigue cracks. A mechanical model is proposed for fretting induced fatigue crack initiation which suggests that this phenomenon is a simple extension of the basic fretting process.

A linear time exact hidden surface algorithm

Abstract: This paper presents a new hidden surface algorithm. Its output is the set of the visible pieces of edges and faces, and is as accurate as the arithmetic precision of the computer. Thus calculating the hidden surfaces for a higher resolution device takes no more time. If the faces are independently and identically distributed, then the execution time is linear in the number of faces. In particular, the execution time does not increase with the depth complexity.This algorithm overlays a grid on the screen whose fineness depends on the number and size of the faces. Edges and faces are sorted into grid cells. Only objects in the same cell can intersect or hide each other. Also, if a face completely covers a cell then nothing behind it in the cell is relevant.Three programs have tested this algorithm. The first verified the variable grid concept on 50,000 intersecting edges. The second verified the linear time, fast speed, and irrelevance of depth complexity for hidden lines on 10,000 spheres. This also tested depth complexities up to 30, and showed that perspective scenes with the farther objects smaller are even faster to calculate. The third verified this for hidden surfaces on 3000 squares.