Tensile ductility and necking of metallic glass

Metallic glasses have a very high strength, hardness and elastic limit. However, they rarely show tensile ductility at room temperature and are considered quasi-brittle materials. Although these amorphous metals are capable of shear flow, severe plastic instability sets in at the onset of plastic deformation, which seems to be exclusively localized in extremely narrow shear bands approximately 10 nm in thickness. Using in situ tensile tests in a transmission electron microscope, we demonstrate radically different deformation behaviour for monolithic metallic-glass samples with dimensions of the order of 100 nm. Large tensile ductility in the range of 23-45% was observed, including significant uniform elongation and extensive necking or stable growth of the shear offset. This large plasticity in small-volume metallic-glass samples did not result from the branching/deflection of shear bands or nanocrystallization. These observations suggest that metallic glasses can plastically deform in a manner similar to their crystalline counterparts, via homogeneous and inhomogeneous flow without catastrophic failure. The sample-size effect discovered has implications for the application of metallic glasses in thin films and micro-devices, as well as for understanding the fundamental mechanical response of amorphous metals.

Characterization of the pathogenic mechanism of a novel BRCA2 variant in a Chinese family

10541

Background: Despite the identification of a large number of sequences in BRCA1/2 mutation analyses, many genetic alterations are classified as variants of unknown significance (VUS). Increasing data demonstrates ethnic variation of BRCA mutation. We report a novel BRCA2 VUS in a Chinese family with multiple breast cancers and characterized it as pathogenic by RNA analysis. Method: Peripheral blood was collected from the breast cancer proband and her family who were suspected to have a pathogenic mutation due the segregation of the disease phenotype and the young age of presentation of breast cancer. DNA and RNA was extracted from the blood. The entire coding regions and flanking introns of BRCA1/2 were screened for germline mutations using full gene sequencing and Multiplex Ligation -dependent Probe Amplification. Variant DNA alteration leading to an aberrant BRCA transcript was demonstrated by RT-PCR of the RNA and Polyacrylamide Gel Electrophoresis. Abnormal bands were cloned and direct sequencing conducted. Results: A germline mutation c.7806–9T>G was identified in the proband at the BRCA2 intron 16. This mutation was also found in 3 of her 4 sibling sisters with early breast cancer. The proband's mother harbored the same BRCA2 mutation in DNA extracted from archival gastric tumor tissues. Computational analyses showed that this mutation might give rise to a cryptic splice site for alternative RNA splicing. To confirm the pathogenicity, RT- PCR using specific primers flanking the cryptic splice site and sequencing was performed on RNA extracted from the proband's blood. Four different sizes of transcripts were found: wild type, r.7806_7874del , r.7806_7976del and r.7806–8_7806-lins. The latter 3 aberrant transcripts were not found in the 30 controls therefore polymorphism is unlikely. The r.7806–8_7806-lins transcript caused a frameshift which created a truncated protein; whereas the other two short transcripts produced shorter BRCA2 protein isoforms. Conclusion: We identified a novel BRCA2 VUS and classified it as pathogenic. Classification of VUS as neutral or pathogenic, particularly in ethnic groups where limited knowledge is known is a challenge. Research on the spectrum of mutations in diversed ethnic groups has important implications on management. [Genbank: DQ889340 ]

No significant financial relationships to disclose.

Polyamorphism in a metallic glass

A metal, or an alloy, can often exist in more than one crystal structure. The face-centred-cubic and body-centred-cubic forms of iron (or steel) are a familiar example of such polymorphism. When metallic materials are made in the amorphous form, is a parallel 'polyamorphism' possible? So far, polyamorphic phase transitions in the glassy state have been observed only in glasses involving directional and open (such as tetrahedral) coordination environments. Here, we report an in situ X-ray diffraction observation of a pressure-induced transition between two distinct amorphous polymorphs in a Ce(55)Al(45) metallic glass. The large density difference observed between the two polyamorphs is attributed to their different electronic and atomic structures, in particular the bond shortening revealed by ab initio modelling of the effects of f-electron delocalization. This discovery offers a new perspective of the amorphous state of metals, and has implications for understanding the structure, evolution and properties of metallic glasses and related liquids. Our work also opens a new avenue towards technologically useful amorphous alloys that are compositionally identical but with different thermodynamic, functional and rheological properties due to different bonding and structural characteristics.

Spectrum of EGFR mutations associated with non-small cell lung cancer in an Asian Chinese population

20055

Background: Somatic mutations in tyrosine kinase (TK) domain of the EGFR gene, predicting for sensitivity to TK inhibition therapy, are over-represented in lung cancer with adenocarcinoma or bronchioloalveolar histology, non-smokers, female gender and East Asian ethnicity. Methods: We prospectively screened for EGFR mutations at exons 19–21 on micro-dissected specimen enriched for tumor cells by direct nucleotide sequencing in Hong Kong Chinese patients. Results: From May 2005 onwards, a total of 27 patients were analyzed. They comprised 11 males and 16 females with a median age of 67 years. Histological diagnoses were adenocarcinoma (n = 22), bronchioloalveolar carcinoma (n = 4) and squamous cell carcinoma (n = 1). Samples included primary tumor (n = 20) as well as metastatic lesions (n = 7). EGFR mutations were detected in 17 patients (63%), the most common being L858R at exon 21 (n = 7) followed by exon 19 deletions (del(746–750) = 3, del(747–751) = 1, del(747–753) = 3) and G719C at exon 18 (n = 1). Two patients showed novel EGFR mutations, namely 4-base pair insertion deletion at exon 19 leading to substitution of Glu746-Leu747 by Val746-Pro747 and three base pair deletion at exon 18 leading to replacement of Glu709-Thr710 by Asp. Furthermore, two patients showed double mutations, including novel S768I at exon 20 in combination with G719C, and novel K860I at exon 21 in combination with L858R. Finally, one patient showed homozygous del(747–753) as detected by sequencing in both primary lung tumor and brain secondary, which might represent loss of heterozygosity. Conclusions: Similar to other series, two hotspots i.e. exon 19 deletion and L858 account for the majority (82%) of detectable EGFR mutations in our patient population. For the rare and novel variants, it would be of interest to document the clinical responsiveness to TK inhibitors gefitinib and erlotinib, so that a more complete picture of cancer genotype phenotype correlation can be achieved.

No significant financial relationships to disclose.

Atomic packing and short-to-medium-range order in metallic glasses

Unlike the well-defined long-range order that characterizes crystalline metals, the atomic arrangements in amorphous alloys remain mysterious at present. Despite intense research activity on metallic glasses and relentless pursuit of their structural description, the details of how the atoms are packed in amorphous metals are generally far less understood than for the case of network-forming glasses. Here we use a combination of state-of-the-art experimental and computational techniques to resolve the atomic-level structure of amorphous alloys. By analysing a range of model binary systems that involve different chemistry and atomic size ratios, we elucidate the different types of short-range order as well as the nature of the medium-range order. Our findings provide a reality check for the atomic structural models proposed over the years, and have implications for understanding the nature, forming ability and properties of metallic glasses.

Use of midazolam and ketamine as sedation for children undergoing minor operative procedures

OBJECTIVES

We used intravenous midazolam and ketamine for children undergoing minor operative procedures with satisfactory results. We aimed to further evaluate its efficacy and adverse effects in pediatric ward setting.

METHODS

This was a prospective study of all children undergoing minor operations with sedation in our pediatric general and oncology wards from July 1998 to June 1999. The procedures included lumber puncture+/-intrathecal chemotherapy, bone marrow aspiration+/-trephine biopsy, central venous catheter removal, skin biopsy, or their combination. All sedation procedures were started with midazolam 0.1 mg/kg and ketamine 1 mg/kg; they were increased gradually to 0.4 and 4 mg/kg, respectively, if necessary. Heart rate and SaO2 were continuously monitored.

RESULTS

Altogether, 369 minor operations were performed in 112 patients (male:female=2:1, median age 6 years, range 5 months-17 years). All achieved adequate sedation, with 96% within 30 s and 75% required just the starting dose. Younger children required a higher dosage (p=0.003 for midazolam, p<0.001 for ketamine). The median recovery time was 87 min, with no association with age, sex, or dosage of sedation, but was longer in patients having hallucination (p=0.001). Adverse effects included tachycardia (27.9%), increased secretion (17.6%), agitation (13.6%), nausea and vomiting (9.2%), hallucination (8.7%), desaturation (8.4%), and cataleptic reaction (0.8%). All desaturation episodes were transient and responded to oxygen supplement alone. None developed bronchospasm or convulsion. Some adverse effects were dose-related. Half of the children who received 0.3 mg/kg midazolam developed desaturation.

CONCLUSIONS

Intravenous midazolam-ketamine can provide rapid, effective, and safe sedation for children undergoing minor operations in ward setting. Adverse effects are mild. Midazolam above 0.3 mg/kg should be used with caution.

Male and female prolactin receptor mRNA expression in the brain of a biparental and a uniparental hamster, phodopus, before and after the birth of a litter

Prolactin receptor (PRL-R) mRNA transcript level was quantified in the choroid plexus (ChP) of a naturally biparental hamster, Phodopus campbelli, and its otherwise similar, yet nonpaternal, sibling species, Phodopus sungorus. Pair-housed males and females on the day before the birth of their first litter (G17), the day after birth (L1), lactation day 5 (L5), and unpaired animals that were sexually naïve, were tested. PRL-R mRNA transcript level relative to total RNA, was evaluated by reverse transcriptase-polymerase chain reaction using primers common to the long- and short-form of the PRL-R in Phodopus. In the ChP, a region implicated in prolactin transport into the central nervous system, females had the expected increase in PRL-R mRNA transcript from dioestrus to L5, consistent with known actions of prolactin. As predicted, males and females of the biparental species were similar, although PRL-R mRNA in naive males was higher than in dioestrus females. Males of the two species also differed as predicted. PRL-R mRNA transcript levels were higher in the biparental males. In addition, P. campbelli males had low PRL-R mRNA at G17 compared to L5. By contrast, non-paternal P. sungorus males had elevated PRL-R mRNA transcript levels on G17 relative to unpaired males. We conclude that PRL-R mRNA in the ChP is differentially regulated before and after birth in a paternal and a nonpaternal male.

Atomic packing of the inherent structure of simple liquids

We report a universal inherent packing structure underlying the simple liquids, the normalized distribution functions of which are independent of temperature and density. The inherent packing state, carrying the maximized configurational entropy, has intrinsic connections with the maximally random jammed state of hard spheres.

Icosahedral short-range order in amorphous alloys

We have characterized the icosahedral short-range order in amorphous solids using local environment probes. Such topological local order is pronounced even in an amorphous alloy that does not form quasicrystalline phases upon crystallization, as demonstrated by the extended x-ray absorption fine structure and x-ray absorption near-edge structure of a Ni-Ag amorphous alloy analyzed through reverse Monte Carlo simulations.

Nanostructured Ti-based multi-component alloys with potential for biomedical applications

A group of Ti(60)Cu(14)Ni(12)Sn(4)M(10) (M=Nb, Ta, Mo) alloys was prepared using arc melting and copper mold casting. The as-prepared alloys have a composite microstructure containing a micrometer-sized dendritic beta-Ti(M) phase dispersed in a nanocrystalline matrix. These new alloys exhibit a low Young's modulus in the range of 59-103 GPa, and a high yield strength of 1037-1755 MPa, together with large plastic strains. The combination of high strength and low elastic modulus offers potential advantages in biomedical applications.

Evaluation of paediatric osteosarcomas by classic cytogenetic and CGH analyses

Classic cytogenetic and comparative genomic hybridisation (CGH) data on osteosarcomas have been reported extensively in the literature. However, the number of paediatric osteosarcoma cases studied below the age of 14 years remains relatively small. This study reports four new cases of paediatric osteosarcoma in patients aged 3 to 13 years, evaluated by classic cytogenetics and CGH analyses. Clonal chromosomal alterations were detected in all the cases and included structural rearrangements at 1p11-13, 1q11, 4q27-33, 6p23-25, 6q16-25, 7p13-22, 7q11-36, 11p10-15, 11q23, 17p11.2-13, 21p11, and 21q11-22. The CGH analysis revealed recurrent gains at 1p, 4q, 17p, and 21q and losses at 3q and 16p. Five amplification sites were observed at 1q11-23, 6p21, 8q13, 8q21.3-24.2, and 17p. The data are discussed and compared with other cytogenetic reports in the literature.

Homogeneity of a supersaturated solid solution

Extended x-ray absorption fine structures, small-angle x-ray scattering, and atomistic model calculations have been employed to probe the homogeneity of the fcc solution created in Ag-Cu, a classical system demonstrating the extension of solubility across the entire miscibility gap through rapid quenching. Our results reveal that in many cases the supersaturated solutions formed have decomposition features on the scale of 1 nm. Conventional diffraction methods are inadequate in determining the level of supersaturation or the uniformity of such solid solution alloys.

Neuronal tolerance to O2 deprivation in drosophila: novel approaches using genetic models

In spite of many advances in monitoring oxygenation and preventing cerebro-vascular accidents, there is still considerable morbidity and mortality from conditions with cerebral blood flow impairment and O2 deprivation leading to hypoxic/ischemic brain injury. Part of this failure is related to the complexity of the cascade of events that ensue after hypoxia or ischemia, but also part of it may be related to the fact that most research in the previous few decades has focused, justifiably, on cerebral vessel disease. However, an important aspect of the cascade is dependent on many factors that are inherent to the nature and response of the tissue itself. Hence, there is more need now for a two-pronged approach to hypoxic/ischemic brain injury, one focusing on vessel disease, its prevention, and treatment, and the other centering on the brain tissue itself and the factors that render neurons and glia more susceptible or more tolerant to a lack of oxygenation. In the past several years, a number of methods, techniques, and animal models have been used to address the response of neurons and glia to lack of oxygen. In this review, we highlight some novel ideas and some results that we and others have obtained, mostly pertaining to the genetic endowment and responses of the central nervous system to O2 deprivation. The role and importance of genetic models, such as the Drosophila melanogaster, are discussed, and an example illustrating how to harness the power of Drosophila genetics is detailed.

Familial deletion of (8)(q24.13q24.22) associated with a normal phenotype

We report a familial deletion of (8q) detected in amniocytes of a fetus with a normal ultrasound and in the phenotypically normal mother, who has now had three pregnancy losses. Chromosome analysis of amniocytes and maternal peripheral blood cells showed an interstitial deletion of (8)(q24.13q24.22), which is distal to the region associated with Langer-Giedion syndrome (LGS) or trichorhinophalangeal (TRP) syndrome. This deletion was confirmed by fluorescence in situ hybridization with a c-myc cosmid clone and chromosome 8 painting library.

Melting mechanisms at the limit of superheating

The atomic-scale details during melting of a surface-free Lennard-Jones crystal were monitored using molecular dynamics simulations. Melting occurs when the superheated crystal spontaneously generates a sufficiently large number of spatially correlated destabilized particles that simultaneously satisfy the Lindemann and Born instability criteria. The accumulation and coalescence of these internal local lattice instabilities constitute the primary mechanism for homogeneous melt nucleation inside the crystal, in lieu of surface nucleation for equilibrium melting. The vibrational and elastic lattice instability criteria as well as the homogeneous nucleation theory all coincide in determining the superheating limit.

Neutrino mass, muon anomalous magnetic moment, and lepton flavor nonconservation

If the generating mechanism for neutrino mass is to account for both the newly observed muon anomalous magnetic moment as well as the present experimental bounds on lepton flavor nonconservation, then the neutrino mass matrix should be almost degenerate and the underlying physics should be observable at future colliders. We illustrate this assertion with two specific examples, and show that gamma(mu;-->egamma)/m5(mu), gamma(tau-->egamma)/m5tau, and gamma(tau-->(mu)gamma)/m5tau are in the ratio ((Delta)m2)2sol/2, ((Delta)m2)2sol/2, and ((Delta)m2)2atm, respectively, where the (Delta)m2 parameters are those of solar and atmospheric neutrino oscillations and bimaximal mixing has been assumed.

Co-existence of alternative forms of 8q gain in cytogenetic clones of three patients with acute myeloid leukemia, pointing to 8q22 approximately 8qter as a region of biologic significance

Clonal trisomy 8 chromosome abnormalities can be detected in 15% of patients with acute myeloid leukemia (AML). The most common form of change is complete gain of the whole chromosome 8, followed by partial gains in unbalanced forms. The biologic consequences of trisomy 8 remain unclear, but a gene dosage effect is suspected. We report on three patients with AML who had alternative forms of chromosome 8 gain in their bone marrow cells. The partial gains resulted from a breakpoint in the chromosome band 8q22. This indicates that the region 8q22 to 8qter may be of particular pathogenetic importance.

Amorphous structures in the immiscible Ag-Ni system

Vapor quenching in the phase-separating Ag-Ni system creates alloys that appear homogeneously amorphous under conventional probes. However, an atomic-level structural analysis based on extended x-ray absorption fine structures in combination with reverse Monte Carlo and molecular dynamics simulations demonstrates that these new phases are characterized by nonuniform, spinodal-like structures on an extremely fine scale. This heterogeneous nature of the structure is directly responsible for the unexpectedly low heat (and temperature) of crystallization observed in calorimetric measurements.

Naturally small seesaw neutrino mass with no new physics beyond the TeV scale

If there is no new physics beyond the TeV energy scale, such as in a theory of large extra dimensions, the smallness of the seesaw neutrino mass, i.e., m(nu) = m(2)(D)/m(N), cannot be explained by a very large m(N). In contrast to previous attempts to find an alternative mechanism for a small m(nu), I show how a solution may be obtained in a simple extension of the standard model, without using any ingredient supplied by the large extra dimensions. It is also experimentally testable at future accelerators.