Cold-temperature deformation of nano-sized tungsten and niobium as revealed by in-situ nano-mechanical experiments

We constructed and developed an in-situ cryogenic nanomechanical system to study small-scale mechanical behavior of materials at low temperatures. Uniaxial compression of two body-centered-cubic (bcc) metals, Nb and W, with diameters between 400 and 1300 nm, was studied at room temperature and at 165 K. Experiments were conducted inside of a Scanning Electron Microscope (SEM) equipped with a nanomechanical module, with simultaneous cooling of sample and diamond tip. Stress-strain data at 165 K exhibited higher yield strengths and more extensive strain bursts on average, as compared to those at 298 K. We discuss these differences in the framework of nano-sized plasticity and intrinsic lattice resistance. Dislocation dynamics simulations with surface-controlled dislocation multiplication were used to gain insight into size and temperature effects on deformation of nano-sized bcc metals

Size-dependent fracture of Si nanowire battery anodes

We use a unique transmission electron microscope (TEM) technique to show that Si nanowires (NWs) with diameters in the range of a few hundred nanometers can be fully lithiated and delithiated without fracture, in spite of the large volume changes that occur in this process. By analyzing the stresses associated with lithiation and delithiation we conclude that the process does not occur by the growth of discrete crystalline phases; rather it occurs by amorphization of the Si NWs followed by diffusion of Li into the structure. By accounting for the large deformation associated with this process and by including the effects of pressure gradients on the diffusion of Li, we show that Si NWs with diameters less than about 300 nm could not fracture even if pre-existing cracks were present in the NW. These predictions appear to be in good agreement with the experiment. Published by Elsevier Ltd.

Novel Size and Surface Oxide Effects in Silicon Nanowires as Lithium Battery Anodes

With its high specific capacity, silicon is a promising anode material for high-energy lithium-ion batteries, but volume expansion and fracture during lithium reaction have prevented implementation. Si nanostructures have shown resistance to fracture during cycling, but the critical effects of nanostructure size and native surface oxide on volume expansion and cycling performance are not understood. Here, we use an ex situ transmission electron microscopy technique to observe the same Si nanowires before and after lithiation and have discovered the impacts of size and surface oxide on volume expansion. For nanowires with native SiO2, the surface oxide can suppress the volume expansion during lithiation for nanowires with diameters <similar to 50 nm. Finite element modeling shows that the oxide layer can induce compressive hydrostatic stress that could act to limit the extent of lithiation. The understanding developed herein of how volume expansion and extent of lithiation can depend on nanomaterial structure is important for the improvement of Si-based anodes.

Stable cycling of double-walled silicon nanotube battery anodes through solid-electrolyte interphase control

Although the performance of lithium ion-batteries continues to improve, their energy density and cycle life remain insufficient for applications in consumer electronics, transport and large-scale renewable energy storage(1-5). Silicon has a large charge storage capacity and this makes it an attractive anode material, but pulverization during cycling and an unstable solid-electrolyte interphase has limited the cycle life of silicon anodes to hundreds of cycles(6-11). Here, we show that anodes consisting of an active silicon nanotube surrounded by an ion-permeable silicon oxide shell can cycle over 6,000 times in half cells while retaining more than 85% of their initial capacity. The outer surface of the silicon nanotube is prevented from expansion by the oxide shell, and the expanding inner surface is not exposed to the electrolyte, resulting in a stable solid-electrolyte interphase. Batteries containing these double-walled silicon nanotube anodes exhibit charge capacities approximately eight times larger than conventional carbon anodes and charging rates of up to 20C (a rate of 1C corresponds to complete charge or discharge in one hour).

Lung cancer patients who are asymptomatic at diagnosis show favorable prognosis: a korean Lung Cancer Registry Study

PURPOSE AND METHODS: The outcomes of lung cancer patients who were asymptomatic at diagnosis have never been reported as part of a large-scale study. A national survey of lung cancer in South Korea registered a total of 8788 patients diagnosed in 2005. We report the results herein, with an emphasis on the prognosis of the asymptomatic lung cancer patients. RESULTS: Adenocarcinoma was the most frequent (36.1%) histopathologic type, followed by squamous cell carcinoma (32.1%), large cell carcinoma (1.5%), and small cell carcinoma (13.5%). In most cases, lung cancer was detected with subjective symptoms, but 6.5% of cases had no symptoms indicative of lung cancer at the time of diagnosis. Compared to symptomatic patients, asymptomatic patients were younger, more often female, non-smokers, and more frequently presented with adenocarcinoma. Initial treatments were surgery (22.1%), radiation therapy (7.8%), chemo-radiation therapy (5.4%), and chemotherapy (38%), while 26.6% of patients were recorded to have supportive care only. Asymptomatic patients received surgery in 60.0% of cases, and they showed significantly longer survival times than symptomatic patients. Absence of symptoms at diagnosis significantly reduced the risk of death from non-small cell lung cancer, regardless of patient age, patient gender, stage at diagnosis, smoking history, or whether treatment was performed, but did not reduce the risk of death from small cell lung cancer. CONCLUSIONS: Adenocarcinoma has grown to be the leading histopathologic type of lung cancer in South Korea. Absence of symptom at diagnosis is a favorable prognostic factor for patients with non-small cell lung cancer

Stabilization of Cyclin-Dependent Kinase 4 by Methionyl-tRNA Synthetase in p16INK4a-Negative Cancer

Although abnormal increases in the level or activity of cyclin-dependent kinase 4 (CDK4) occur frequently in cancer, the underlying mechanism is not fully understood. Here, we show that methionyl-tRNA synthetase (MRS) specifically stabilizes CDK4 by enhancing the formation of the complex between CDK4 and a chaperone protein. Knockdown of MRS reduced the CDK4 level, resulting in G0/G1 cell cycle arrest. The effects of MRS on CDK4 stability were more prominent in the tumor suppressor p16INK4a-negative cancer cells because of the competitive relationship of the two proteins for binding to CDK4. Suppression of MRS reduced cell transformation and the tumorigenic ability of a p16INK4a-negative breast cancer cell line in vivo. Further, the MRS levels showed a positive correlation with those of CDK4 and the downstream signals at high frequency in p16INK4a-negative human breast cancer tissues. This work revealed an unexpected functional connection between the two enzymes involving protein synthesis and the cell cycle