Large-Scale Integration of Nanoelectromechanical Systems for Gas Sensing Applications

We have developed arrays of nanomechanical systems (NEMS) by large-scale integration, comprising thousands of individual nanoresonators with densities of up to 6 million NEMS per square centimeter. The individual NEMS devices are electrically coupled using a combined series-parallel configuration that is extremely robust with respect to lithographical defects and mechanical or electrostatic-discharge damage. Given the large number of connected nanoresonators, the arrays are able to handle extremely high input powers (>1 W per array, corresponding to <1 mW per nanoresonator) without excessive heating or deterioration of resonance response. We demonstrate the utility of integrated NEMS arrays as high-performance chemical vapor sensors, detecting a part-per-billion concentration of a chemical warfare simulant within only a 2 s exposure period

Tensor Product and Permutation Branes on the Torus

We consider B-type D-branes in the Gepner model consisting of two minimal models at k=2. This Gepner model is mirror to a torus theory. We establish the dictionary identifying the B-type D-branes of the Gepner model with A-type Neumann and Dirichlet branes on the torus.Comment: 26 page

Matrix Factorizations and Homological Mirror Symmetry on the Torus

We consider matrix factorizations and homological mirror symmetry on the torus T^2 using a Landau-Ginzburg description. We identify the basic matrix factorizations of the Landau-Ginzburg superpotential and compute the full spectrum, taking into account the explicit dependence on bulk and boundary moduli. We verify homological mirror symmetry by comparing three-point functions in the A-model and the B-model.Comment: 41 pages, 9 figures, v2: reference added, minor corrections and clarifications, version published in JHE

Bulk flows in Virasoro minimal models with boundaries

The behaviour of boundary conditions under relevant bulk perturbations is studied for the Virasoro minimal models. In particular, we consider the bulk deformation by the least relevant bulk field which interpolates between the mth and (m-1)st unitary minimal model. In the presence of a boundary this bulk flow induces an RG flow on the boundary, which ensures that the resulting boundary condition is conformal in the (m-1)st model. By combining perturbative RG techniques with insights from defects and results about non-perturbative boundary flows, we determine the endpoint of the flow, i.e. the boundary condition to which an arbitrary boundary condition of the mth theory flows to.Comment: 34 pages, 6 figures. v4: Typo in fig. 2 correcte

Bounds for State Degeneracies in 2D Conformal Field Theory

In this note we explore the application of modular invariance in 2-dimensional CFT to derive universal bounds for quantities describing certain state degeneracies, such as the thermodynamic entropy, or the number of marginal operators. We show that the entropy at inverse temperature 2 pi satisfies a universal lower bound, and we enumerate the principal obstacles to deriving upper bounds on entropies or quantum mechanical degeneracies for fully general CFTs. We then restrict our attention to infrared stable CFT with moderately low central charge, in addition to the usual assumptions of modular invariance, unitarity and discrete operator spectrum. For CFT in the range c_left + c_right < 48 with no relevant operators, we are able to prove an upper bound on the thermodynamic entropy at inverse temperature 2 pi. Under the same conditions we also prove that a CFT can have a number of marginal deformations no greater than ((c_left + c_right) / (48 - c_left - c_right)) e^(4 Pi) - 2.Comment: 23 pages, LaTeX, minor change

Matrix factorisations and D-branes on K3

D-branes on K3 are analysed from three different points of view. For deformations of hypersurfaces in weighted projected space we use geometrical methods as well as matrix factorisation techniques. Furthermore, we study the D-branes on the T^4/\Z_4 orbifold line in conformal field theory. The behaviour of the D-branes under deformations of the bulk theory are studied in detail, and good agreement between the different descriptions is found.Comment: 35 pages, no figure

Whirling Hexagons and Defect Chaos in Hexagonal Non-Boussinesq Convection

We study hexagon patterns in non-Boussinesq convection of a thin rotating layer of water. For realistic parameters and boundary conditions we identify various linear instabilities of the pattern. We focus on the dynamics arising from an oscillatory side-band instability that leads to a spatially disordered chaotic state characterized by oscillating (whirling) hexagons. Using triangulation we obtain the distribution functions for the number of pentagonal and heptagonal convection cells. In contrast to the results found for defect chaos in the complex Ginzburg-Landau equation and in inclined-layer convection, the distribution functions can show deviations from a squared Poisson distribution that suggest non-trivial correlations between the defects.Comment: 4 mpg-movies are available at http://www.esam.northwestern.edu/~riecke/lit/lit.html submitted to New J. Physic

The Effect of Lattice Vibrations on Substitutional Alloy Thermodynamics

A longstanding limitation of first-principles calculations of substitutional alloy phase diagrams is the difficulty to account for lattice vibrations. A survey of the theoretical and experimental literature seeking to quantify the impact of lattice vibrations on phase stability indicates that this effect can be substantial. Typical vibrational entropy differences between phases are of the order of 0.1 to 0.2 k_B/atom, which is comparable to the typical values of configurational entropy differences in binary alloys (at most 0.693 k_B/atom). This paper describes the basic formalism underlying ab initio phase diagram calculations, along with the generalization required to account for lattice vibrations. We overview the various techniques allowing the theoretical calculation and the experimental determination of phonon dispersion curves and related thermodynamic quantities, such as vibrational entropy or free energy. A clear picture of the origin of vibrational entropy differences between phases in an alloy system is presented that goes beyond the traditional bond counting and volume change arguments. Vibrational entropy change can be attributed to the changes in chemical bond stiffness associated with the changes in bond length that take place during a phase transformation. This so-called ``bond stiffness vs. bond length'' interpretation both summarizes the key phenomenon driving vibrational entropy changes and provides a practical tool to model them.Comment: Submitted to Reviews of Modern Physics 44 pages, 6 figure

Fabrication of endothelial cell-laden carrageenan microfibers for microvascularized bone tissue engineering applications

ecent achievements in the area of tissue engineering (TE) have enabled the development of three-dimensional (3D) cell-laden hydrogels as in vitro platforms that closely mimic the 3D scenario found in native tissues. These platforms are extensively used to evaluate cellular behavior, cell-cell interactions, and tissue-like formation in highly defined settings. In this study, we propose a scalable and flexible 3D system based on microsized hydrogel fibers that might be used as building blocks for the establishment of 3D hydrogel constructs for vascularized bone TE applications. For this purpose, chitosan (CHT) coated κ-carrageenan (κ-CA) microfibers were developed using a two-step procedure involving ionotropic gelation (for the fiber formation) of κ-CA and its polyelectrolyte complexation with CHT (for the enhancement of fiber stability). The performance of the obtained fibers was assessed regarding their swelling and stability profiles, as well as their ability to carry and, subsequently, promote the outward release of microvascular-like endothelial cells (ECs), without compromising their viability and phenotype. Finally, the possibility of assembling and integrating these cell-laden fibers within a 3D hydrogel matrix containing osteoblast-like cells was evaluated. Overall, the obtained results demonstrate the suitability of the microsized κ-CA fibers to carry and deliver phenotypically apt microvascular-like ECs. Furthermore, it is shown that it is possible to assemble these cell-laden microsized fibers into 3D heterotypic hydrogels constructs. This in vitro 3D platform provides a versatile approach to investigate the interactions between multiple cell types in controlled settings, which may open up novel 3D in vitro culture techniques to better mimic the complexity of tissues.Authors thank the Portuguese Foundation for Science and Technology (FCT) for the personal grants SFRH/BD/42968/2008 through the MIT-Portugal Program (SMM) and SFRH/BD/64070/2009 (EGP). The research leading to these results has received funding from the European Union's Seventh Framework Programme (FP7/2007-2013) under grant agreement no REGPOT-CT2012-316331-POLARIS and MIT/ECE/0047/2009 project

The impact of physical activity on fatigue and quality of life in lung cancer patients: a randomised controlled trial protocol

Background: People with lung cancer have substantial symptom burden and more unmet needs than the general cancer population. Physical activity (PA) has been shown to positively influence quality of life (QOL), fatigue and daily functioning in the curative treatment of people with breast and colorectal cancers and lung diseases, as well as in palliative settings. A randomised controlled trial (RCT) is needed to determine if lung cancer patients benefit from structured PA intervention. The Physical Activity in Lung Cancer (PAL) trial is designed to evaluate the impact of a 2-month PA intervention on fatigue and QOL in patients with non-resectable lung cancer. Biological mechanisms will also be studied.Methods/design: A multi-centre RCT with patients randomised to usual care or a 2-month PA programme, involving supervised PA sessions including a behavioural change component and home-based PA. QOL questionnaires, disease and functional status and body composition will be assessed at baseline, 2, 4 and 6 months follow-up. The primary endpoint is comparative levels of fatigue between the 2 arms. Secondary endpoints include: QOL, functional abilities and physical function. Exploratory endpoints include: anxiety, depression, distress, dyspnoea, PA behaviour, fitness, hospitalisations, survival, cytokines and insulin-like growth factor levels.Discussion: This study will provide high-level evidence of the effect of PA programmes on cancer-related fatigue and QOL in patients with advanced lung cancer. If positive, the study has the potential to change care for people with cancer using a simple, inexpensive intervention to improve their QOL and help them maintain independent function for as long as possible.Trial registration: Australian New Zealand Clinical Trials Registry No. ACTRN12609000971235. © 2012 Dhillon et al.; licensee BioMed Central Ltd