632 research outputs found
pH-, thermo- and electrolyte-responsive polymer gels derived from a well-defined, RAFT-synthesized, poly(2-vinyl-4,4-dimethylazlactone) homopolymer via one-pot post-polymerization modification
Well-defined stimulus-responsive polymer gels were prepared from poly(2-vinyl-4,4-dimethylazlatone) (PVDMA) via one-pot post-polymerization modification. VDMA homopolymers were reacted with diamine crosslinking agents and functional 1° or 2° amines to form polymer gels that swelled in organic solvents and, in many cases, aqueous solutions. A series of functional amine reagents, including N,N-dimethylethylenediamine (DMEDA), N,N-diethylethylenediamine (DEEDA), morpholine, 3-morpholinopropylamine (MPPA) and tetrahydrofurfurylamine (THFA), were chosen as functional amines to produce polymer gels containing environmentally sensitive species. 13C solid-state NMR and FTIR spectroscopic measurements confirmed complete conversion of the reactive scaffolds. pH-dependent swelling behavior at ambient temperature was observed in DMEDA-, DEEDA- and MPPA-modified hydrogels. Kinetic studies showed the swelling behaviors of DMEDA-modified hydrogels were regulated by cross-linker type and concentration in acidic water (pH = 4) at ambient temperature. The swelling ratio of hydrogels modified by DEEDA, MPPA and THFA also depended strongly on temperature, indicating successful synthesis of thermoresponsive gels. Furthermore, the concentration of added sodium sulfate played a significant role with respect to the swelling properties of MPPA-modified hydrogels. These smart materials may be of interest in the biomedical field as well as in other applications
Mechano-responsive polymer solutions based on CO2 supersaturation: shaking-induced phase transitions and self-assembly or dissociation of polymeric nanoparticles
Mechanical stimulation of supersaturated aqueous CO2 solutions is accompanied by a pH increase within seconds. In solutions of tailored homo- and AB diblock copolymers this is exploited to induce micelle formation, or, taking advantage of an aqueous upper critical solution temperature transition, nanoparticle disassembly
An objective based classification of aggregation techniques for wireless sensor networks
Wireless Sensor Networks have gained immense popularity in recent years due to their ever increasing capabilities and wide range of critical applications. A huge body of research efforts has been dedicated to find ways to utilize limited resources of these sensor nodes in an efficient manner. One of the common ways to minimize energy consumption has been aggregation of input data. We note that every aggregation technique has an improvement objective to achieve with respect to the output it produces. Each technique is designed to achieve some target e.g. reduce data size, minimize transmission energy, enhance accuracy etc. This paper presents a comprehensive survey of aggregation techniques that can be used in distributed manner to improve lifetime and energy conservation of wireless sensor networks. Main contribution of this work is proposal of a novel classification of such techniques based on the type of improvement they offer when applied to WSNs. Due to the existence of a myriad of definitions of aggregation, we first review the meaning of term aggregation that can be applied to WSN. The concept is then associated with the proposed classes. Each class of techniques is divided into a number of subclasses and a brief literature review of related work in WSN for each of these is also presented
Strong polarization-induced reduction of addition energies in single-molecule nanojunctions
We address polarization-induced renormalization of molecular levels in
solid-state based single-molecule transistors and focus on an organic conjugate
molecule where a surprisingly large reduction of the addition energy has been
observed. We have developed a scheme that combines a self-consistent solution
of a quantum chemical calculation with a realistic description of the screening
environment. Our results indeed show a large reduction, and we explain this to
be a consequence of both (a) a reduction of the electrostatic molecular
charging energy and (b) polarization induced level shifts of the HOMO and LUMO
levels. Finally, we calculate the charge stability diagram and explain at a
qualitative level general features observed experimentally.Comment: 9 pages, 5 figure
Correlation of interfacial bonding mechanism and equilibrium conductance of molecular junctions
We report theoretical investigations on the role of interfacial bonding
mechanism and its resulting structures to quantum transport in molecular wires.
Two bonding mechanisms for the Au-S bond in an
Au(111)/1,4-benzenedithiol(BDT)/Au(111) junction were identified by ab initio
calculation, confirmed by a recent experiment, which, we showed, critically
control charge conduction. It was found, for Au/ BDT/Au junctions, the hydrogen
atom, bound by a dative bond to the Sulfur, is energetically non-dissociative
after the interface formation. The calculated conductance and junction
breakdown forces of H-non-dissociative Au/BDT/Au devices are consistent with
the experimental values, while the H-dissociated devices, with the interface
governed by typical covalent bonding, give conductance more than an order of
magnitude larger. By examining the scattering states that traverse the
junctions, we have revealed that mechanical and electric properties of a
junction have strong correlation with the bonding configuration. This work
clearly demonstrates that the interfacial details, rather than previously
believed many-body effects, is of vital importance for correctly predicting
equilibrium conductance of molecular junctions; and manifests that the
interfacial contact must be carefully understood for investigating quantum
transport properties of molecular nanoelectronics.Comment: 18 pages, 6 figures, 2 tables, to be appeared in Frontiers of Physics
9(6), 780 (2014
Highly Conducting pi-Conjugated Molecular Junctions Covalently Bonded to Gold Electrodes
We measure electronic conductance through single conjugated molecules bonded
to Au metal electrodes with direct Au-C covalent bonds using the scanning
tunneling microscope based break-junction technique. We start with molecules
terminated with trimethyltin end groups that cleave off in situ resulting in
formation of a direct covalent sigma bond between the carbon backbone and the
gold metal electrodes. The molecular carbon backbone used in this study consist
of a conjugated pi-system that has one terminal methylene group on each end,
which bonds to the electrodes, achieving large electronic coupling of the
electrodes to the pi-system. The junctions formed with the prototypical example
of 1,4-dimethylenebenzene show a conductance approaching one conductance
quantum (G0 = 2e2/h). Junctions formed with methylene terminated oligophenyls
with two to four phenyl units show a hundred-fold increase in conductance
compared with junctions formed with amine-linked oligophenyls. The conduction
mechanism for these longer oligophenyls is tunneling as they exhibit an
exponential dependence of conductance with oligomer length. In addition,
density functional theory based calculations for the Au-xylylene-Au junction
show near-resonant transmission with a cross-over to tunneling for the longer
oligomers.Comment: Accepted to the Journal of the American Chemical Society as a
Communication
Relating Energy Level Alignment and Amine-Linked Single Molecule Junction Conductance
Using photoemission spectroscopy, we determine the relationship between
electronic energy level alignment at a metal-molecule interface and
single-molecule junction transport data. We measure the position of the highest
occupied molecular orbital (HOMO) relative to the Au metal Fermi level for
three 1,4-benzenediamine derivatives on Au(111) and Au(110) with ultraviolet
and resonant x-ray photoemission spectroscopy. We compare these results to
scanning tunnelling microscope based break-junction measurements of single
molecule conductance and to first-principles calculations. We find that the
energy difference between the HOMO and Fermi level for the three molecules
adsorbed on Au(111) correlate well with changes in conductance, and agree well
with quasiparticle energies computed from first-principles calculations
incorporating self-energy corrections. On the Au(110) which present Au atoms
with lower-coordination, critical in break-junction conductance measurements,
we see that the HOMO level shifts further from the Fermi level. These results
provide the first direct comparison of spectroscopic energy level alignment
measurements with single molecule junction transport data
The Role of Ultrasound in teaching Clinical Anatomy to First year Medical Students
Abstract Introduction: Undergraduate medical education training has recently shifted towards making content relevant and applicable for future clinical practice. However, students often encounter difficulties in visualizing the functional living human and apply clinically relevant anatomy content. Hence, the aim of this study is to evaluate the role and efficacy of ultrasound in teaching clinical anatomy to first year medical students
Quantum Smoluchowski equation: Escape from a metastable state
We develop a quantum Smoluchowski equation in terms of a true probability
distribution function to describe quantum Brownian motion in configuration
space in large friction limit at arbitrary temperature and derive the rate of
barrier crossing and tunneling within an unified scheme. The present treatment
is independent of path integral formalism and is based on canonical
quantization procedure.Comment: 10 pages, To appear in the Proceedings of Statphys - Kolkata I
Identification of Bruton's tyrosine kinase as a therapeutic target in acute myeloid leukemia
Bruton's tyrosine kinase (BTK) is a cytoplasmic protein found in all hematopoietic cell lineages except for T cells. BTK mediates signalling downstream of a number of receptors. Pharmacological targeting of BTK using ibrutinib (previously PCI-32765) has recently shown encouraging clinical activity in a range of lymphoid malignancies. This study reports for the first time that ibrutinib inhibits blast proliferation from human acute myeloid leukaemia (AML) and that treatment with ibrutinib significantly augmented cytotoxic activities of standard AML chemotherapy cytarabine or daunorubicin. Here we describe that BTK is constitutively phosphorylated in the majority of AML samples tested, with BTK phosphorylation correlating highly with the cell's cytotoxic sensitivity towards ibrutinib. BTK targeted RNAi knock-down reduced colony forming capacity of primary AML blasts and proliferation of AML cell lines. We showed ibrutinib binds at nanomolar range to BTK. Furthermore, we also showed ibrutinib's anti-proliferative effects in AML are mediated via an inhibitory effect on downstream nuclear factor-ÎşB (NF-ÎşB) survival pathways. Moreover, ibrutinib inhibited AML cell adhesion to bone marrow stroma. Furthermore, these effects of ibrutinib in AML were seen at comparable concentrations efficacious in chronic lymphocytic leukemia (CLL). These results provide a biologic rationale for clinical evaluation of BTK inhibition in AML patients
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