Modeling and analysis of fault tolerant multistage interconnection networks

Performance and reliability are two of the most crucial issues in today's high-performance instrumentation and measurement systems. High speed and compact density multistage interconnection networks (MINs) are widely-used subsystems in different applications. New performance models are proposed to evaluate a novel fault tolerant MIN arrangement, thereby assuring performance and reliability with high confidence level. A concurrent fault detection and recovery scheme for MINs is considered by rerouting over redundant interconnection links under stringent real-time constraints for digital instrumentation such as sensor networks. A switch architecture for concurrent testing and diagnosis is proposed. New performance models are developed and used to evaluate the compound effect of fault tolerant operation (inclusive of testing, diagnosis, and recovery) on the overall throughput and delay. Results are shown for single transient and permanent stuck-at faults on links and storage units in the switching elements. It is shown that performance degradation due to fault tolerance is graceful while performance degradation without fault recovery is unacceptable.     

Role of donor and recipient antigen-presenting cells in priming and maintaining T cells with indirect allospecificity

BACKGROUND: It has been suggested that the sensitization of recipient T lymphocytes against peptides derived from allogeneic major histocompatibility complex (MHC) antigens in the context of self-MHC molecules may contribute to the pathogenesis of chronic allograft rejection. The purpose of this study was to quantitate and characterize the indirect alloresponse in renal transplantation. METHODS: An HLA-A2-negative patient whose A2-positive kidney transplant failed as a result of chronic rejection was selected for this study. T-cell clones were raised using a cocktail of peptides corresponding to polymorphic regions of the A2 sequence and studied by measuring their proliferation using [3H]thymidine incorporation. The presence in vivo of HLA-A2-specific T cells was assessed using limiting dilution analysis. RESULTS: T-cell clones were specific for a single peptide of HLA-A2, residues 92-120, and restricted by HLA-DRB1*1502. The frequency of interleukin-2-secreting T cells specific for this A2 peptide was 1:86,000, only 2-fold lower than that measured against the recall antigen tetanus toxoid. Capitalizing on the similarity of the donor and recipient DR15 alleles (DRB1*1501 and 1502), the question was addressed as to how these T cells had been primed in vivo. Although the large majority of clones responded to A2 synthetic peptide presented by both DR15 alleles, only 3 of 10 clones responded to cells co-expressing DRB1*1501 and A2. CONCLUSION: These data suggest that antigen presentation by recipient APCs is responsible for maintaining T cells with indirect allospecificity in vivo and that, in the context of partial DR matching, indirect presentation by the parenchymal cells of the graft may serve to induce tolerance in T cells with indirect allospecificity.     

Delayed acquisition of high-avidity anti-cytomegalovirus antibody is correlated with prolonged antigenemia in solid organ transplant recipients

Previous studies have demonstrated that maturation of cytomegalovirus (CMV)-specific antibodies in solid organ transplant recipients is delayed after primary CMV infection. To investigate the clinical significance of this finding, the avidity indices of anti-CMV antibody were determined in parallel with other serologic and virologic parameters in serial serum samples from 24 solid organ transplant recipients who had primary CMV infection that began during the first 3 months after transplantation. The data obtained show that a delay in antibody maturation is significantly correlated with a long persistence of positive antigenemia.     

Pelvic ultrasonography in normal girls and in girls with pubertal precocity

Small bowel allograft rejection in large animals has yet to be well defined. There are no specific early signs of graft rejection. The present experiments were undertaken to compare acute small bowel allograft rejection in pigs with and without FK506 and also to examine the usefulness of mucosal biopsies. Thirty-six outbred Large-White pigs were divided into (1) group 1 (n = 9): nonimmunosuppressed recipients; (2) group 2 (n = 8): FK506-immunosuppressed recipients; (3) group 3 (n = 2): autotransplant controls; and (4) donors (n = 17). Orthotopic small bowel transplantations were performed with Thiry-Vella loops for daily biopsies. The survival rate of group 2 was significantly longer than that of group 1 (P < 0.05). One best survivor in group 2 was killed at postoperative day (POD) 365. Treatment by FK506 prevented rejection, but most of the pigs died of pneumonia. In group 1, rejection began on POD 3 and progressed to severe rejection rapidly within 7 days. In group 2, rejection began from POD 6 to POD 8, but either remained mild or spontaneously improved. The differences in the routine laboratory data and the tumor necrosis factor-alpha level were not evident between the groups. Histological studies of repeated graft biopsies are thus considered to be essential for detecting signs of graft rejection.     

A line-based parallel memory for QCA implementation

Quantum-dot cellular automata (QCA) has been widely advocated as a new device architecture for nanotechnology. Using QCA, the innovative design of digital systems can be achieved by exploiting the so-called capability of processing-in-wire, i.e., signal manipulation proceeds at the same time as propagation. QCA systems require low power together with the potential for high density and regularity. These features make QCA an attractive technology for manufacturing memories in which the in-wire paradigm can be exploited for storage purposes. This paper proposes a novel parallel memory architecture for QCA implementation. This architecture is based on storing information on a QCA line by changing the direction of signal flow among three clocking zones. Timing of these zones requires two additional clocks to implement a four-step process for reading/writing data to the memory. Its operation has been verified by simulation. It is shown that the requirements for clocking, number of zones, as well as the underlying CMOS circuitry are significantly reduced compared with previous QCA parallel architectures.     

Mechanical properties of porous ceramics in compression: On the transition between elastic,brittle, and cellular behavior

This paper deals with the uniaxial compression behavior of porous ceramics within a wide range of porosity, varying from 30 to 75 vol%. The load–displacement curves recorded on porous alumina samples showed a transition between a typical brittle behavior at porosity fractions below 60 vol% and a damageable, cellular-like behavior, at higher porosity fractions. This transition in fracture mode was confirmed by in situ compression tests in an X-ray tomograph. Based on a simple model taking into account the competition between the crack length initiating from spherical pores and the mean distance between pores, the porosity at which the transition took place was estimated. The influence of the pore size also depended on the volume fraction of pores: no size effect was noted at the lowest porosity whereas a statistical effect on the size of the solid walls was observed at higher porosity, with an increase in fracture strength with small pores.     

Study of the effect of prolonged magnetic stirring on the physico-chemical surface properties of nanometric transition alumina

This article reports the study of a transition nanometric alumina both as such and after prolonged magnetic stirring in bi-distilled water. Stirring was effective in inducing a significant reduction of starting particles agglomeration and modification of the surface properties of the material. The formation of an Al(OH)₃ (gibbsite) phase after magnetic stirring in water was detected by means of XRD on powdered samples. Correspondingly, Infra Red spectrum of magnetically stirred alumina outgassed at 150 °C showed a band at ca. 3300 cm⁻¹, ascribable to the hydroxide phase, which decomposes at higher temperature. Differential thermal analysis and thermogravimetry also showed a different thermal behaviour between the two materials, in that magnetically stirred alumina presents a broad endothermic peak at about 280 °C accompanied by an abrupt mass loss (ca. 0.5% of the initial weight), due to dehydration of the hydroxide phase.