Gentile statistics and restricted partitions

In a recent paper (Tran et al, Ann. Phys.311, 204 (2004)), some asymptotic number theoretical results on the partitioning of an integer were derived exploiting its connection to the quantum density of states of a many-particle system. We generalise these results to obtain an asymptotic formula for the restricted or coloured partitions pks (n), which is the number of partitions of an integer n into the summand of sth powers of integers such that each power of a given integer may occur utmost k times. While the method is not rigorous, it reproduces the well-known asymptotic results for s = 1 apart from yielding more general results for arbitrary values of s

A Study Aimed at Characterizing the Interfacial Structure in a Tin-Silver Solder on Nickel-Coated Copper Plate during Aging

This paper highlights the interfacial structure of tin-silver (Sn-3·5Ag) solder on nickel-coated copper pads during aging performance studies at a temperature of 150°C for up to 96 h. Experimental results revealed the as-solidified solder bump made from using the lead-free solder (Sn-3·5Ag) exhibited or showed a thin layer of the tin-nickel-copper intermetallic compound (IMC) at the solder/substrate interface. This includes a sub-layer having a planar structure immediately adjacent to the Ni-coating and a blocky structure on the inside of the solder. Aging performance studies revealed the thickness of both the IMC layer and the sub-layer, having a planar structure, to increase with an increase in aging time. The observed increase was essentially non-linear. Fine microscopic cracks were observed to occur at the interfaces of the planar sub-layer and the block sub-layer

Mechanical Behavior of a Magnesium Alloy Nanocomposite under Conditions of Static Tension and Dynamic Fatigue

In this paper, the intrinsic influence of nano-alumina particulate (Al2O3p) reinforcements on microstructure, microhardness, tensile properties, tensile fracture, cyclic stress-controlled fatigue, and final fracture behavior of a magnesium alloy is presented and discussed. The unreinforced magnesium alloy (AZ31) and the reinforced composite counterpart (AZ31/1.5 vol.% Al2O3) were manufactured by solidification processing followed by hot extrusion. The elastic modulus, yield strength, and tensile strength of the nanoparticle-reinforced magnesium alloy were noticeably higher than the unreinforced counterpart. The ductility, quantified by elongation-to-failure, of the composite was observably lower than the unreinforced monolithic counterpart (AZ31). The nanoparticle-reinforced composite revealed improved cyclic fatigue resistance over the entire range of maximum stress at both the tested load ratios. Under conditions of fully reversed loading (R = −1) both materials showed observable degradation in behavior quantified in terms of cyclic fatigue life. The conjoint influence of reinforcement, processing, intrinsic microstructural features and loading condition on final fracture behavior is presented and discussed

Understanding the Influence of Pressure and Radial Loads on Stress and Displacement Response of a Rotating Body: The Automobile Wheel

This paper highlights the use of the finite element technique for analyzing stress and displacement distributions in wheels of automotive vehicles when subject to the conjoint influence of inflation pressure and radial load. The most commonly used considerations in the design of the rotating body are elucidated. A potentially viable technique for finite element modeling of radial wheel, subjected to loading, is highlighted. The extrinsic influence of inflation pressure on performance of the rotating body, that is, the wheel, is rationalized

Single-cell RNA-sequencing reveals Transcriptional Changes and Clonal Architecture associated with Post-Transplant Relapse in Acute Myeloid Leukemia

"Acute myeloid leukemia (AML) is a malignancy characterized by overproduction of myeloid precursors at the expense of more differentiated, functional hematopoietic cells, resulting in anemia, thrombocytopenia, and neutropenia. Despite initial sensitivity to chemotherapy, a majority of patients with AML ultimately relapse. Among the challenges associated with relapse, post-allogeneic stem cell transplant relapse is particularly intractable because of our relative lack of understanding - and thus lack of effective treatment options - of the underlying mechanisms."--IntroductionZiheng Xu (1), Christopher A. Miller (2, 3), Sridhar N. Srivatsan (2), Catrina C. Fronick (3), Robert S. Fulton (3), Timothy J. Ley (2, 3, 4), and Allegra A. Petti (2, 3) ; 1. Washington University School of Medicine. 2. Division of Oncology, Washington University School of Medicine. 3. McDonnell Genome Institute, Washington University School of Medicine. 4. Department of Genetics, Washington University School of Medicine.Includes bibliographical reference

Synthesis of an aluminum alloy metal matrix composite using powder metallurgy : role of sintering parameters

Powder metallurgy-based metal matrix composites (MMCs) are widely chosen and used for the development of components in the fields spanning aerospace, automotive and even electronic components. Engineered MMCs are known to offer a high strength-to-weight (σ/ρ) ratio. In this research study, we synthesized cylindrical sintered samples of a ceramic particle-reinforced aluminum metal matrix using the technique of powder metallurgy. The samples for the purpose of testing, examination and analysis were made by mixing aluminum powder with powders of silicon carbide and aluminum oxide or alumina. Four varieties of aluminum composite were synthesized for a different volume percent of the ceramic particle reinforcement. The hybrid composite contained 2 vol.% and 7 vol.% of silicon carbide and 3 vol.% and 8 vol.% of alumina with aluminum as the chosen metal matrix. Homogeneous mixtures of the chosen powders were prepared using conventional ball milling. The homogeneous powder mixture was then cold compacted and subsequently sintered in a tubular furnace in an atmosphere of argon gas. Five different sintering conditions (combinations of temperature and sintering time) were chosen for the purpose of this study. The density and hardness of each sintered specimen were carefully evaluated. Cold compression tests were carried out for the purpose of determining the compressive strength of the engineered MMC. The sintered density and hardness of the aluminum MMCs varied with the addition of ceramic particle reinforcements. An increase in the volume fraction of the alumina particles to the Al/SiC mixture reduced the density, hardness and compressive strength. The sintering condition was optimized for the aluminum MMCs based on the hardness, densification parameter and cold compressive strength. The proposed powder metallurgy-based route for the fabrication of the aluminum matrix composite revealed a noticeable improvement in the physical and mechanical properties when compared one-on-one with commercially pure aluminum

One in Four Individuals of African-American Ancestry Harbors a 5.5kb Deletion at chromosome 11q13.1

Cloning and sequencing of 5.5kb deletion at chromosome 11q13.1 from the HeLa cells, tumorigenic hybrids and two fibroblast cell lines has revealed homologous recombination between AluSx and AluY resulting in the deletion of intervening sequences. Long-range PCR of the 5.5kb sequence in 494 normal lymphocyte samples showed heterozygous deletion in 28.3% of African- American ancestry samples but only in 4.8% of Caucasian samples (p<0.0001). This observation is strengthened by the copy number variation (CNV) data of the HapMap samples which showed that this deletion occurs in 27% of YRI (Yoruba – West African) population but none in non- African populations. The HapMap analysis further identified strong linkage disequilibrium between 5 single nucleotide polymorphisms and the 5.5kb deletion in the people of African ancestry. Computational analysis of 175kb sequence surrounding the deletion site revealed enhanced flexibility, low thermodynamic stability, high repetitiveness, and stable stem-loop/ hairpin secondary structures that are hallmarks of common fragile sites

HT2003-47477 AN INVESTIGATION OF COPPER DISSOLUTION AND THE FORMATION OF INTERMETALLIC COMPOUNDS IN MOLTEN TIN AND Tin-Silver SOLDERS

ABSTRACT This paper presents an experimental study of copper dissolution in molten tin and tin-silver (Sn-Ag) solders and the formation and presence of the Cu-Sn intermetallic compound at solder/copper interfaces. During the experiments, copper (99.9% pure) samples, coated with a RMA flux, were dipped vertically in a molten solder for different time periods ranging from 5 seconds to 10 minutes. The molten solder was maintained at temperatures of 232 o C, 250 o C and 300 o C for pure tin and 221 o C, 250 o C, and 300 o C for Sn-3.5%Ag respectively. The samples were then cut, cleaned and cold mounted in epoxy at ambient temperature. Mechanical grinding, finish polishing, etching, and optical metallographic procedures were utilized for examining the microstructures of the polished and etched samples. The average thickness of the intermetallic compound and the amount of copper dissolved was determined. Experimental results indicate the temperature of molten solder to control the rate of dissolution of copper and the formation and presence of intermetallic compounds at the interfaces. At a given temperature of the solder temperature, the rate of dissolution of copper in the solder revealed a rising trend with an increase in dwell time of copper in the solder. For short contact time periods, the dissolution rate is low and the thickness of the intermetallic compound is small. With an increase in dwell time, the dissolution rate of copper rapidly increases and eventually reaches a plateau. Initiation of dissolution of copper causes a layer of the Sn-Cu intermetallic compound to form around the copper substrate. This in turn prevents direct contact of the copper substrate with the molten solder. The rate of formation of the layer of intermetallic compound reveals a similar trend. Based on experimental results, the kinetic parameters involved in governing the growth of the intermetallic were determined for the two solders. The parameters can be used to estimate the kinetics of copper dissolution and intermetallic compound formation during soldering

Reconstitution of long and short patch mismatch repair reactions using Saccharomyces cerevisiae proteins

This study demonstrates mismatch repair (MMR) reactions reconstituted in vitro with purified Saccharomyces cerevisiae proteins. Biochemical analysis of MMR in vitro showed that MMR required mispair binding by the MutS homolog 2–MutS homolog 6 complex and corresponded to the Exonuclease 1-dependent subpathway of MMR. The reactions observed involved the formation of long excision tracts whose length was consistent with the length of MMR-dependent gene conversion tracts in vivo. The availability of this reconstituted MMR reaction now allows the wealth of mutations affecting MMR generated from the genetic analysis of S. cerevisiae MMR mechanisms in vivo to be used in biochemical reconstitution studies whose ultimate goal is to reconstitute MMR linked to both DNA replication and recombination