6,916 research outputs found
Effects of Cardiac Structural Remodelling During Heart Failure on Cardiac Excitation â Insights from a Heterogeneous 3D Model of the Rabbit Atria
Heart failure is a leading cause of morbidity and mortality in the western world. One of the effects of heart failure is the structural remodelling of cardiac tissue, including tissue dilation and development of fibrosis. It is therefore important to study these changes and their effect on cardiac activity, in order to gain a better understanding of the underlying mechanisms in arrhythmogenesis, which will hopefully enable us to develop better treatments for heart failure. In this study we developed biophysically detailed models of the rabbit atria for normal and heart failure conditions. These models were used to study the effects of structural remodelling of heart failure on cardiac excitation wave conduction. Anatomical reconstructions of the control and heart failure hearts were based on contrast enhanced micro-CT imaging. Fibre orientation was extracted from the control and heart failure datasets. Effects of heart failure geometry on the activation pattern of atrial excitation waves were analyzed. It was found that atrial activation time increased from the control to the heart failure case in both isotropic and anisotropic conditions, which is attributed primarily to the dilation of tissue caused by heart failure
DolphinAtack: Inaudible Voice Commands
Speech recognition (SR) systems such as Siri or Google Now have become an
increasingly popular human-computer interaction method, and have turned various
systems into voice controllable systems(VCS). Prior work on attacking VCS shows
that the hidden voice commands that are incomprehensible to people can control
the systems. Hidden voice commands, though hidden, are nonetheless audible. In
this work, we design a completely inaudible attack, DolphinAttack, that
modulates voice commands on ultrasonic carriers (e.g., f > 20 kHz) to achieve
inaudibility. By leveraging the nonlinearity of the microphone circuits, the
modulated low frequency audio commands can be successfully demodulated,
recovered, and more importantly interpreted by the speech recognition systems.
We validate DolphinAttack on popular speech recognition systems, including
Siri, Google Now, Samsung S Voice, Huawei HiVoice, Cortana and Alexa. By
injecting a sequence of inaudible voice commands, we show a few
proof-of-concept attacks, which include activating Siri to initiate a FaceTime
call on iPhone, activating Google Now to switch the phone to the airplane mode,
and even manipulating the navigation system in an Audi automobile. We propose
hardware and software defense solutions. We validate that it is feasible to
detect DolphinAttack by classifying the audios using supported vector machine
(SVM), and suggest to re-design voice controllable systems to be resilient to
inaudible voice command attacks.Comment: 15 pages, 17 figure
Understanding Household Behavioral Risk Factors for Diarrheal Disease in Dar es Salaam: A Photovoice Community Assessment
Whereas Tanzania has seen considerable improvements in water and sanitation infrastructure over the past 20 years, the country still faces high rates of childhood morbidity from diarrheal diseases. This study utilized a qualitative, cross-sectional, modified Photovoice method to capture daily activities of Dar es Salaam mothers. A total of 127 photographs from 13 households were examined, and 13 interviews were conducted with household mothers. The photographs and interviews revealed insufficient hand washing procedures, unsafe disposal of wastewater, uncovered household drinking water containers, a lack of water treatment prior to consumption, and inappropriate toilets for use by small children. The interviews revealed that mothers were aware and knowledgeable of the risks of certain household practices and understood safer alternatives, yet were restricted by the perceived impracticality and financial constraints to make changes. The results draw attention to the real economic and behavioral challenges faced in reducing the spread of disease
Continuous-flow precipitation of hydroxyapatite in ultrasonic microsystems
This paper describes the continuous-flow precipitation of hydroxyapatite Ca5(PO4)3OH (HAp) in two ultrasonic microreactors using diluted aqueous solutions of calcium and phosphate at 37 °C. Precipitation of HAp was first carried out in a tubular microreactor immersed in an ultrasonic bath, where single-phase (laminar) flow and segmented gas-liquid flow were both evaluated. The single-phase flow study was then conducted in a novel microfluidic device developed at MIT. It consists of a Teflon stack microreactor with an integrated piezoelectric element (Teflon microreactor), thereby allowing the direct transmission of ultrasound to the reactor. Both microsystems produce single-phased calcium-deficient carbonated HAp under near-physiological conditions of temperature and pH. In addition, particle aggregation and primary particle size were significantly reduced in the segmented-flow tubular microreactor and in the Teflon microreactor. The as-prepared particles mostly consisted of rod-like shape nanoparticles with dimensions below 100 nm in length and around 20 nm in width. Further, the microreactors used yielded HAp particles with improved characteristics text was removed, namely higher crystallinity and less carbonate contamination, when compared to the HAp particles produced in a stirred tank batch reactor.This work was supported by the Portuguese Foundation for Science and Technology (SFRH/BD/42992/2008) through the MIT-Portugal Program, Bioengineering Systems Focus Area. The authors are thankful to Dr. Speakman for his help with the X-ray measurements and with the interpretation of the results. S.K. acknowledges funding from the Swiss National Science Foundation (SNF)
Process intensification and optimization for hydroxyapatite nanoparticles production
Precipitation processes are widely used in industry for the production of particulate solids. Efficient mixing of the reagents is of major importance for the chemical and physical nature of the synthesized particles. Recently, microreactors have been studied to overcome homogeneity problems found when using stirred tank batch reactors. The present work investigated an ultrasonic tubular microreactor for the continuous-flow precipitation of hydroxyapatite (HAp), both in single-phase flow (SPF) and in gasâliquid flow (GLF). HAp nanoparticles were yielded for both configurations under near-physiological conditions of pH and temperature. The as-prepared particles, especially those that were prepared under GLF, show improved characteristics compared to commercial powder or powder obtained in a stirred tank batch reactor. Primary particles are smaller, particle shape is more homogeneous, and the aggregation degree of the particles is lower
Near Horizon Limits of Massless BTZ and Their CFT Duals
We consider the massless BTZ black hole and show that it is possible to take
its "near horizon" limit in two distinct ways. The first one leads to a null
self-dual orbifold of AdS3 and the second to a spacelike singular AdS3/Z_K
orbifold in the large K limit, the "pinching orbifold". We show that from the
dual 2d CFT viewpoint, the null orbifold corresponds to the p^+=0 sector of the
Discrete Light-Cone Quantisation (DLCQ) of the 2d CFT where a chiral sector of
the CFT is decoupled, while the pinching orbifold corresponds to taking an
infinite mass gap limit in both the right and left sectors of the 2d CFT,
essentially leaving us with the states L_0=\bar L_0=c/24 only. In the latter
case, one can combine the near horizon limit with sending the 3d Planck length
l_P to zero, or equivalently the dual CFT central charge c to infinity. We
provide preliminary evidence that in that case some nontrivial dynamics may
survive the limit.Comment: 22 pages, no figures, v2: minor improvements, references adde
Experimental evidence of stochastic resonance without tuning due to non Gaussian noises
In order to test theoretical predictions, we have studied the phenomenon of
stochastic resonance in an electronic experimental system driven by white non
Gaussian noise. In agreement with the theoretical predictions our main findings
are: an enhancement of the sensibility of the system together with a remarkable
widening of the response (robustness). This implies that even a single resonant
unit can reach a marked reduction in the need of noise tuning.Comment: 4 pages, 3 figure
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