307 research outputs found
Sub 20 nm Silicon Patterning and Metal Lift-Off Using Thermal Scanning Probe Lithography
The most direct definition of a patterning process' resolution is the
smallest half-pitch feature it is capable of transferring onto the substrate.
Here we demonstrate that thermal Scanning Probe Lithography (t-SPL) is capable
of fabricating dense line patterns in silicon and metal lift-off features at
sub 20 nm feature size. The dense silicon lines were written at a half pitch of
18.3 nm to a depth of 5 nm into a 9 nm polyphthalaldehyde thermal imaging layer
by t-SPL. For processing we used a three-layer stack comprising an evaporated
SiO2 hardmask which is just 2-3 nm thick. The hardmask is used to amplify the
pattern into a 50 nm thick polymeric transfer layer. The transfer layer
subsequently serves as an etch mask for transfer into silicon to a nominal
depth of 60 nm. The line edge roughness (3 sigma) was evaluated to be less than
3 nm both in the transfer layer and in silicon. We also demonstrate that a
similar three-layer stack can be used for metal lift-off of high resolution
patterns. A device application is demonstrated by fabricating 50 nm half pitch
dense nickel contacts to an InAs nanowire.Comment: 7 pages, 5 figures, to be published in JVST
Observation of a continuous phase transition in a shape-memory alloy
Elastic neutron-scattering, inelastic x-ray scattering, specific-heat, and
pressure-dependent electrical transport measurements have been made on single
crystals of AuZn and Au_{0.52}Zn_{0.48} above and below their martensitic
transition temperatures (T_M=64K and 45K, respectively). In each composition,
elastic neutron scattering detects new commensurate Bragg peaks (modulation)
appearing at Q = (1.33,0.67,0) at temperatures corresponding to each sample's
T_M. Although the new Bragg peaks appear in a discontinuous manner in the
Au_{0.52}Zn_{0.48} sample, they appear in a continuous manner in AuZn.
Surprising us, the temperature dependence of the AuZn Bragg peak intensity and
the specific-heat jump near the transition temperature are in favorable accord
with a mean-field approximation. A Landau-theory-based fit to the pressure
dependence of the transition temperature suggests the presence of a critical
endpoint in the AuZn phase diagram located at T_M*=2.7K and p*=3.1GPa, with a
quantum saturation temperature \theta_s=48.3 +/- 3.7K.Comment: 6 figure
Scanning force microscopy in the dynamic mode using microfabricated capacitive sensors
We report on the first successful operation of a scanning force microscope using microfabricated capacitive force sensors. The sensors, which are made from single crystal silicon on insulator wafers, consist of a cantilever spring with integrated tip at the free end and an electrically insulated counter electrode. Dynamic force gradient sensing is the preferred operating mode. Here, tipβsample interactions are detected by letting the sensor act as a resonator in a phase controlled oscillator setup and measuring corresponding shifts of the oscillation frequency. Experiments were performed in vacuum using a standard tunneling microscope. A Cr grating on a quartz substrate served as the test sample. Topographic images showing details on a 10 nm scale were obtained operating at a constant force gradient of the order of 0.01 N/m. In addition, critical design parameters are discussed based on an analysis of the electromechanical properties of the sensors
Fermi Surface as a Driver for the Shape-Memory Effect in AuZn
Martensites are materials that undergo diffusionless, solid-state
transitions. The martensitic transition yields properties that depend on the
history of the material and may allow it to recover its previous shape after
plastic deformation. This is known as the shape-memory effect (SME). We have
succeeded in identifying the primary electronic mechanism responsible for the
martensitic transition in the shape-memory alloy AuZn by using Fermi-surface
measurements (de Haas-van Alphen oscillations) and band-structure calculations.
This strongly suggests that electronic band structure is an important
consideration in the design of future SME alloys
Lenalidomide treatment and prognostic markers in relapsed or refractory chronic lymphocytic leukemia: data from the prospective, multicenter phase-II CLL-009 trial
Efficacy of lenalidomide was investigated in 103 patients with relapsed/refractory chronic lymphocytic leukemia (CLL) treated on the prospective, multicenter randomized phase-II CLL-009 trial. Interphase cytogenetic and mutational analyses identified TP53 mutations, unmutated IGHV, or del(17p) in 36/96 (37.5%), 68/88 (77.3%) or 22/92 (23.9%) patients. The overall response rate (ORR) was 40.4% (42/104). ORRs were similar irrespective of TP53 mutation (36.1% (13/36) vs 43.3% (26/60) for patients with vs without mutation) or IGHV mutation status (45.0% (9/20) vs 39.1% (27/68)); however, patients with del(17p) had lower ORRs than those without del(17p) (21.7% (5/22) vs 47.1% (33/70); P=0.049). No significant differences in progression-free survival and overall survival (OS) were observed when comparing subgroups defined by the presence or absence of high-risk genetic characteristics. In multivariate analyses, only multiple prior therapies (greater than or equal to3 lines) significantly impacted outcomes (median OS: 21.2 months vs not reached; P=0.019). This analysis indicates that lenalidomide is active in patients with relapsed/refractory CLL with unfavorable genetic profiles, including TP53 inactivation or unmutated IGHV. (ClinicalTrials.gov identifier: NCT00963105)
A Minimal Threshold of c-di-GMP Is Essential for Fruiting Body Formation and Sporulation in Myxococcus xanthus
Generally, the second messenger bis-(3β-5β)-cyclic dimeric GMP (c-di-GMP) regulates the switch between motile and sessile lifestyles in bacteria. Here, we show that c-di-GMP is an essential regulator of multicellular development in the social bacterium Myxococcus xanthus. In response to starvation, M. xanthus initiates a developmental program that culminates in formation of spore-filled fruiting bodies. We show that c-di-GMP accumulates at elevated levels during development and that this increase is essential for completion of development whereas excess c-di-GMP does not interfere with development. MXAN3735 (renamed DmxB) is identified as a diguanylate cyclase that only functions during development and is responsible for this increased c-di-GMP accumulation. DmxB synthesis is induced in response to starvation, thereby restricting DmxB activity to development. DmxB is essential for development and functions downstream of the Dif chemosensory system to stimulate exopolysaccharide accumulation by inducing transcription of a subset of the genes encoding proteins involved in exopolysaccharide synthesis. The developmental defects in the dmxB mutant are non-cell autonomous and rescued by co-development with a strain proficient in exopolysaccharide synthesis, suggesting reduced exopolysaccharide accumulation as the causative defect in this mutant. The NtrC-like transcriptional regulator EpsI/Nla24, which is required for exopolysaccharide accumulation, is identified as a c-diGMP receptor, and thus a putative target for DmxB generated c-di-GMP. Because DmxB can beβat least partiallyβfunctionally replaced by a heterologous diguanylate cyclase, these results altogether suggest a model in which a minimum threshold level of c-di-GMP is essential for the successful completion of multicellular development in M. xanthus
Effect of laser treatment on the attachment and viability of mesenchymal stem cell responses on shape memory NiTi alloy
The objectives of this study were to investigate the effect of laser-induced surface features on the morphology, attachment and viability of mesenchymal stem cells (MSCs) at different periods of time, and to evaluate the biocompatibility of different zones: laser-melted zone (MZ), heat-affected zone (HAZ) and base metal (BM) in laser-treated NiTi alloy. The surface morphology and composition were studied by scanning electron microscope (SEM) and X-ray photoemission spectroscopy (XPS), respectively. The cell morphology was examined by SEM while the cell counting and viability measurements were done by hemocytometer and 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) colorimetric assay. The results indicated that the laser-induced surface features, such as surface roughening, presence of anisotropic dendritic pattern and complete surface Ni oxidation were beneficial to improve the biocompatibility of NiTi as evidenced by the highest cell attachment (4 days of culture) and viability (7 days of culture) found in the MZ. The biocompatibility of the MZ was the best, followed by the BM with the HAZ being the worst. The defective and porous oxide layer as well as the coarse grained structure might attribute to the inferior cell attachment (4 days of culture) and viability (7 days of culture) on the HAZ compared with the BM which has similar surface morphology. ΓΒ© 2014 Elsevier B.V
A c-di-GMP Effector System Controls Cell Adhesion by Inside-Out Signaling and Surface Protein Cleavage
In Pseudomonas fluorescens Pf0-1 the availability of inorganic phosphate (Pi) is an environmental signal that controls biofilm formation through a cyclic dimeric GMP (c-di-GMP) signaling pathway. In low Pi conditions, a c-di-GMP phosphodiesterase (PDE) RapA is expressed, depleting cellular c-di-GMP and causing the loss of a critical outer-membrane adhesin LapA from the cell surface. This response involves an inner membrane protein LapD, which binds c-di-GMP in the cytoplasm and exerts a periplasmic output promoting LapA maintenance on the cell surface. Here we report how LapD differentially controls maintenance and release of LapA: c-di-GMP binding to LapD promotes interaction with and inhibition of the periplasmic protease LapG, which targets the N-terminus of LapA. We identify conserved amino acids in LapA required for cleavage by LapG. Mutating these residues in chromosomal lapA inhibits LapG activity in vivo, leading to retention of the adhesin on the cell surface. Mutations with defined effects on LapD's ability to control LapA localization in vivo show concomitant effects on c-di-GMP-dependent LapG inhibition in vitro. To establish the physiological importance of the LapD-LapG effector system, we track cell attachment and LapA protein localization during Pi starvation. Under this condition, the LapA adhesin is released from the surface of cells and biofilms detach from the substratum. This response requires c-di-GMP depletion by RapA, signaling through LapD, and proteolytic cleavage of LapA by LapG. These data, in combination with the companion study by Navarro et al. presenting a structural analysis of LapD's signaling mechanism, give a detailed description of a complete c-di-GMP control circuitβfrom environmental signal to molecular output. They describe a novel paradigm in bacterial signal transduction: regulation of a periplasmic enzyme by an inner membrane signaling protein that binds a cytoplasmic second messenger
Temporal Controls of the Asymmetric Cell Division Cycle in Caulobacter crescentus
The asymmetric cell division cycle of Caulobacter crescentus is orchestrated by an elaborate gene-protein regulatory network, centered on three major control proteins, DnaA, GcrA and CtrA. The regulatory network is cast into a quantitative computational model to investigate in a systematic fashion how these three proteins control the relevant genetic, biochemical and physiological properties of proliferating bacteria. Different controls for both swarmer and stalked cell cycles are represented in the mathematical scheme. The model is validated against observed phenotypes of wild-type cells and relevant mutants, and it predicts the phenotypes of novel mutants and of known mutants under novel experimental conditions. Because the cell cycle control proteins of Caulobacter are conserved across many species of alpha-proteobacteria, the model we are proposing here may be applicable to other genera of importance to agriculture and medicine (e.g., Rhizobium, Brucella)
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