Band Structure and Quantum Conductance of Nanostructures from Maximally-Localized Wannier Functions: The Case of Functionalized Carbon Nanotubes

We have combined large-scale, $\Gamma$-point electronic-structure calculations with the maximally-localized Wannier functions approach to calculate efficiently the band structure and the quantum conductance of complex systems containing thousands of atoms while maintaining full first-principles accuracy. We have applied this approach to study covalent functionalizations in metallic single-walled carbon nanotubes. We find that the band structure around the Fermi energy is much less dependent on the chemical nature of the ligands than on the $sp^3$ functionalization pattern disrupting the conjugation network. Common aryl functionalizations are more stable when paired with saturating hydrogens; even when paired, they still act as strong scattering centers that degrade the ballistic conductance of the nanotubes already at low degrees of coverage.Comment: To be published in Phys. Rev. Let

On the Distribution of Salient Objects in Web Images and its Influence on Salient Object Detection

It has become apparent that a Gaussian center bias can serve as an important prior for visual saliency detection, which has been demonstrated for predicting human eye fixations and salient object detection. Tseng et al. have shown that the photographer's tendency to place interesting objects in the center is a likely cause for the center bias of eye fixations. We investigate the influence of the photographer's center bias on salient object detection, extending our previous work. We show that the centroid locations of salient objects in photographs of Achanta and Liu's data set in fact correlate strongly with a Gaussian model. This is an important insight, because it provides an empirical motivation and justification for the integration of such a center bias in salient object detection algorithms and helps to understand why Gaussian models are so effective. To assess the influence of the center bias on salient object detection, we integrate an explicit Gaussian center bias model into two state-of-the-art salient object detection algorithms. This way, first, we quantify the influence of the Gaussian center bias on pixel- and segment-based salient object detection. Second, we improve the performance in terms of F1 score, Fb score, area under the recall-precision curve, area under the receiver operating characteristic curve, and hit-rate on the well-known data set by Achanta and Liu. Third, by debiasing Cheng et al.'s region contrast model, we exemplarily demonstrate that implicit center biases are partially responsible for the outstanding performance of state-of-the-art algorithms. Last but not least, as a result of debiasing Cheng et al.'s algorithm, we introduce a non-biased salient object detection method, which is of interest for applications in which the image data is not likely to have a photographer's center bias (e.g., image data of surveillance cameras or autonomous robots)

Características del programa de maestría de Balcarce

La Unidad Integrada Balcarce (UIB) constituye un centro de generación y tranferenciatecnológicay deformación de recursos humanos en ciencias agropecuarias, merced al asentamiento común y a los esfuerzos coordinados de la Estación Experimental Agropecuaria (EEA) de Balcarce, dependiente del Instituto Nacional de Tecnología agropecuaria (INTA) y la Facultad de Ciencias Agrarias (FCA) de Balcarce, dependiente de la Universidad Nacional de Mar del Plata (UNMdP). La particular concepción cooperativa de ambas unidades les permite cumplir sus respectivos objetivos y complementarse convenientemente en la realización de las actividades que así lo requieren.Academia Nacional de Agronomía y Veterinaria (ANAV

Características del programa de maestría de Balcarce

La Unidad Integrada Balcarce (UIB) constituye un centro de generación y tranferenciatecnológicay deformación de recursos humanos en ciencias agropecuarias, merced al asentamiento común y a los esfuerzos coordinados de la Estación Experimental Agropecuaria (EEA) de Balcarce, dependiente del Instituto Nacional de Tecnología agropecuaria (INTA) y la Facultad de Ciencias Agrarias (FCA) de Balcarce, dependiente de la Universidad Nacional de Mar del Plata (UNMdP). La particular concepción cooperativa de ambas unidades les permite cumplir sus respectivos objetivos y complementarse convenientemente en la realización de las actividades que así lo requieren.Academia Nacional de Agronomía y Veterinaria (ANAV

Axisymmetric equilibrium and stability analysis in Alcator C-Mod, including effects of current profile, measurement noise and power supply saturation

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Nuclear Science and Engineering, 2009.Cataloged from PDF version of thesis.Includes bibliographical references (p. 147-150).The vertical position of elongated tokamak plasmas is unstable on the time scale of the eddy currents in the axisymmetric conducting structures. In the absence of feedback control, the plasma would drift vertically and quench on the wall, a situation known as Vertical Displacement Event (VDE), with serious consequences for machine integrity. As tokamaks approach reactor regimes, VDE's cannot be tolerated: vertical feedback control must be robust against system uncertainty and the occurrence of noise and disturbances. At the same time, adaptive routines should be in place to handle unexpected events. The problem of robust control of the vertical position can be formulated in terms of identifying which variables affect vertical stability and which ones are not directly controlled/controllable; identifying the physical region of these variables, and the corresponding most unstable equilibria; and designing the control system to stabilize all equilibria with sufficient margin. The margin should be enough to allow the system to tolerate realistic scenarios of noise and disturbances. A set of metrics is introduced to characterize the problem of vertical stability: the stability margin describes the plasma-wall interaction and the open-loop growth rate; the maximum controllable displacement looks at the vertical stabilization power supplies and their ability to handle noise and off-normal events; the gain and phase margins quantify the linear stability of the feedback control loop.(cont.) The dependence of these metrics on relevant plasma parameters is proven with analytic calculations and numerical simulations: in particular, it is shown that the stability margin is a decreasing function of the plasma internal inductance, for a given plasma elongation. An upper bound of the value of the internal inductance is derived and validated with database analysis, which describes the most unstable equilibrium for given values of the external elongation and the edge safety factor. The stability metrics are evaluated for typical and ITER-like C-Mod plasmas to give an example of the C-Mod operational space and of feasible control conditions. The vertical stabilization system should be able to tolerate realistic scenarios of noise and disturbances. The main sources of noise and pick-ups in Alcator C-Mod are identified and their effects on the measurement and control of the vertical position are evaluated. Broadband noise may affect controllability of C-Mod plasmas at limit elongations and may become an issue with high-order controllers, therefore two applications of Kalman filters are investigated. A Kalman filter is compared to a state observer based on the pseudo-inverse of the measurement matrix and proves to be a better candidate for state reconstruction for vertical stabilization, provided adequate models of the system, the inputs, the intrinsic and measurement noise and an adequate set of diagnostic measurements are available. A single-input single-output application of the filter for the vertical observer rejects high frequency noise without destabilizing high-elongation plasmas, however does not match the performance of an optimized low-pass filter.(cont.) Aggressive control targets and large off-normal events can cause a control current to rail. The magnetic topology is consequently perturbed and the plasma might become uncontrollable. An adaptive anti-saturation control routine is demonstrated which avoids an impending saturation by interpolating in real-time to a safe equilibrium. This approach becomes necessary when poor redundancy of control coils may require mid-shot pulse rescheduling, as opposed to an adaptation in control.by Marco Ferrara.Ph.D

Digital plasma control system and Alcasim simulation code for Alcator C-Mod

Includes bibliographical references (p. 105-107).Thesis (S.M.)--Massachusetts Institute of Technology, Dept. of Nuclear Engineering, 2005.Abstract The Alcator C-Mod control system was upgraded to digital architecture DPCS (Digital Plasma Control System). The main features of the digital system are the high flexibility, robustness and maintainability. The hardware consists of low-latency digitizers, a single processor Xeon server and DAC output cards. The software is a set of IDL routines. In the current version of the software, DPCS is emulating the PID controller of the previous control system Hybrid, but some advanced and adaptive features have already been implemented, for example the compensation of the input offsets. DPCS has been operating successfully since the beginning of the 2004-2005 experimental campaign. One of the advantages of a digital control system is that a simulator can be embedded in the system. We programmed a Matlab-Simulink simulator Alcasim for Alcator C-Mod. The simulator is a versatile tool to model the tokamak and the plasma, to interface with the database of the real experiments and to test new control algorithms, while running open loop and closed loop simulations. The powerful block-diagram language of Simulink allows to easily update the various components of the feedback loop, should the need arise. Preliminary results from the simulations of real shots are presented and discussed.by Marco Ferrara.S.M

Novel materials, computational spectroscopy, and multiscale simulation in nanoscale photovoltaics

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Materials Science and Engineering, 2013.Cataloged from PDF version of thesis.Includes bibliographical references (p. 96-104).Photovoltaic (PV) solar cells convert solar energy to electricity using combinations of semiconducting sunlight absorbers and metallic materials as electrical contacts. Novel nanoscale materials introduce new paradigms for ultrathin, lightweight, solution processable PV as an alternative to conventional Si technology. For example, the ability to use deposition methods not viable in conventional inorganic PV is particularly exciting as products like paper, textiles, automobiles, and building materials could be coated with PV devices, thus making solar cells ubiquitous. In addition, the optical absorption, band gap, and charge carrier mobility of nanoscale materials can be tuned by tailoring their chemistry or using quantum confinement effects, thus creating novel opportunities for efficient and inexpensive solar cells. From the viewpoint of the fundamental processes involved in PV operation, nanoscale PV poses additional challenges due to the formation of strongly bound electron-hole pairs (excitons) upon photoabsorption requiring the presence of semiconductor heterointerfaces within the active layer to dissociate excitons and generate charge carriers. Such interfaces are known as donor-acceptor (D-A) interfaces, and their presence leads to correlated exciton and charge dynamics in nanoscale PV. Material combinations suitable for nanoscale PV can be predicted using atomistic quantum mechanical calculations, which further enable the computation of a small number of spectroscopic quantities necessary to estimate the power conversion efficiency. Our work shows the computational design of two novel classes of materials for nanoscale PV displaying optical absorption, stability, tunability, and carrier mobility superior to materials employed so far in nanoscale PV. To this end, we employed simulation techniques generally falling under the umbrella of ab initio atomistic electronic structure methods, including density functional theory (DFT) and the GW-Bethe-Salpeter approach. Proof-of-concept PV devices were fabricated and tested within our group and in collaboration with other experimental research groups. The two material families studied in this thesis include carbon based materials (both in nanoscale and bulk form) and two-dimensional monolayers such as graphene, reduced graphene oxide, boron nitride, and transition metal dichalcogenides. Our work demonstrates the feasibility of novel PV devices with a range of benefits employing such materials. It further develops a framework to accurately predict exciton dissociation at D-A interfaces and estimate efficiencies in nanoscale PV. Beyond our work on nanoscale materials, we introduce a combination of methods to enable simulation of nanoscale PV across time and length scales. We discuss modeling of subpicosecond dynamics at D-A interfaces, device-scale transport of excitons, charge carriers, and photons, and macroscopic sunlight management by arranging solar panels to best couple with the Sun's trajectory. We elaborate on the latter point and discuss our work on simulation and fabrication of macroscopic three-dimensional PV structures with promise to deliver a range of benefits for solar energy conversion, including reduced seasonal and latitude sensitivity and a doubling of peak power generation hours. Taken together, this thesis advances the computational design of nanoscale PV systems and introduces novel families of materials and PV structures with technological promise for next-generation PV. This thesis document is organized as follows: Chapter 1 and Chapter 2 introduce, respectively, nanoscale PV and ab initio atomistic simulation methods employed in this work. Chapter 3 is the core of our work on novel families of materials for nanoscale PV, and Chapter 4 illustrates multi-scale simulation methods in nanoscale PV as well as our work on three-dimensional PV. The key results are briefly summarized in Chapter 5.by Marco Bernardi.Ph.D

Quantitative dynamic modeling of transcriptional networks of embryonic stem cells using integrated framework of Pareto optimality and energy balance

Thesis (Ph. D.)--Harvard-MIT Division of Health Sciences and Technology, 2009.Cataloged from PDF version of thesis.Includes bibliographical references (p. 252-256).Embryonic Stem Cells (ESCs) are pluripotent and thus are considered the "cell type of choice". ESCs exhibit several phenotypic traits (e.g., proliferation, differentiation, apoptosis, necrosis, etc.) and when differentiated into a particular lineage they can perform an array of functions (e.g., protein secretion, detoxification, energy production). Typically, these cellular objectives compete against each other because of thermodynamic, stoichiometric and mass balance constraints. Analysis of transcriptional regulatory networks and metabolic networks in ESCs thus requires both a nonequilibrium thermodynamic and mass balance framework for designing and understanding complex ESC network approach as well as an optimality approach which can take cellular objectives into account simultaneously. The primary goal of this thesis was to develop an integrated energy and mass balance-based multi objective framework for a transcriptional regulatory network model for ESCs. The secondary goal was to utilize the developed framework for large-scale metabolic flux profiling of hepatic and ESC metabolic networks. Towards the first aim we first developed a complete dynamic pluripotent network model for ESCs which integrates several different master regulators of pluripotency such as transcription factors Oct4, Sox2, Nanog, Klf4, Nacl, Rexl, Daxl, cMyc, and Zfp281, and obtained the dynamic connectivity matrix between various pluripotency related gene promoters and transcription factors. The developed model fully describes the self-renewal state of embryonic stem cells.(cont.) Next, we developed a transcriptional network model framework for ESCs that incorporates multiobjective optimality-based energy balance analysis. This framework predicts cofactor occupancy, network architecture and feedback memory of ESCs based on energetic cost. The integrated nonequilibrium thermodynamics and multiobjective-optimality network analysis-based approach was further utilized to explain the significance of transcriptional motifs defined as small regulatory interaction patterns that regulate biological functions in highly interacting cellular networks. Our results yield evidence that dissipative energetics is the underlying criteria used during evolution for motif selection and that biological systems during transcription tend towards evolutionary selection of subgraphs which produces minimum specific heat dissipation, thereby explaining the frequency of some motifs. Significantly, the proposed energetic hypothesis uncovers a mechanism for environmental selection of motifs, provides explanation for topological generalization of subgraphs into complex networks and enables identification of new functionalities for rarely occurring motifs. Towards the secondary goal, we have developed a multiobjecive optimization-based approach that couples the normalized constraint with both energy and flux balance-based metabolic flux analysis to explain certain features of metabolic control of hepatocytes, which is relevant to the response of hepatocytes and liver to various physiological stimuli and disease states. We also utilized this approach to obtain an optimal regimen for ESC differentiation into hepatocytes.(cont.) The presented framework may establish multiobjective optimality-based thermodynamic analysis as a backbone in designing and understanding complex network systems, such as transcriptional, metabolic and protein interaction networks.by Marco A. Avila.Ph.D

Small bowel adenocarcinoma in a patient with Coeliac disease: A case report

Coeliac disease is a chronic inflammatory disease of the gut with increased risk of gastrointestinal malignancy. Although enteropathy T-lymphoma is the most common neoplasm in patient affected by coeliac disease, an increased frequency of small bowel carcinoma has been described. We present a case of jejunal carcinoma in a patient suffering for coeliac disease in which gastrointestinal and extraintestinal symptoms of disease developed although he was treated with a gluten-free diet

One year effectiveness of an app-based treatment for urinary incontinence in comparison to care as usual in Dutch general practice:A pragmatic randomised controlled trial over 12 months

OBJECTIVE: To assess the long-term effectiveness of app-based treatment for female stress, urgency, or mixed urinary incontinence (UI) compared to care-as-usual in primary care. DESIGN: A pragmatic, randomised controlled, superiority trial. SETTING: Primary care in the Netherlands from 2015 to 2018, follow-up at 12 months. POPULATION: Women with ≥2 UI-episodes per week, access to mobile apps, wanting treatment. 262 women randomised equally to app or care-as-usual; 89 (68%) and 83 (63%) attended one year follow-up. INTERVENTIONS: The standalone app included conservative management for UI with motivation aids (e.g., reminders). Care-as-usual delivered according to the Dutch GP guideline for UI. MAIN OUTCOME MEASURES: Effectiveness assessed by the change in symptom severity score (ICIQ-UI-SF) and the change in quality of life (ICIQ-LUTS-QoL) with linear regression on an intention-to-treat basis. RESULTS: Clinically relevant improvement of UI severity for both app (-2.17 ± 2.81) and care-as-usual (-3.43 ± 3.6), with a non-significant mean difference of 0.903 (-0.66 to 1.871). CONCLUSION: App-based treatment is a viable alternative to care-as-usual for UI in primary care in terms of effectiveness after one year