Hand powered portable ultraviolet sterilizing water bottle with active UV dose sensing

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, September 2007 [first author]; and, (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, June 2006 [second author].Includes bibliographical references (p. 71).A portable hand powered water sterilization device was created to address a portion of the growing epidemic of global water contamination. As being more supply chain independent and having an active dose sensing component that monitors the water to insure sterilization, our device boasts far more than any current off-the-shelf devices. The device is completely hand powered via a hand crank generator. A spermicidal ultraviolet light bulb, rated at 253.7nm (UV-C), was integrated with a common NalgeneTM water bottle. Along with the bulb, UV. dose sensing electronics and a hand crank generator were incorporated as well, with the generator supplying power to both the bulb and the photodiode circuitry. Results show that eradication of common waterborne bacteria, protozoa, and viruses occurs after cranking the generator for approximately 41 seconds in clear water and up to 65 seconds in turbid water. The total weight added to the water bottle was less than a pound.by Chandan Das and Justin Holland.S.B

Laser induced reentrant freezing in two-dimensional attractive colloidal systems

The effects of an externally applied one-dimensional periodic potential on the freezing/melting behaviour of two-dimensional systems of colloidal particles with a short-range attractive interaction are studied using Monte Carlo simulations. In such systems, incommensuration results when the periodicity of the external potential does not match the length-scale at which the minimum of the attractive potential occurs. To study the effects of this incommensuration, we consider two different models for the system. Our simulations for both these models show the phenomenon of reentrant freezing as the strength of the periodic potential is varied. Our simulations also show that different exotic phases can form when the strength of the periodic potential is high, depending on the length-scale at which the minimum of the attractive pair-potential occurs.Comment: 24 pages (including figures) in preprint forma

Routes to spatiotemporal chaos in the rheology of nematogenic fluids

With a view to understanding the "rheochaos" observed in recent experiments in a variety of orientable fluids, we study numerically the equations of motion of the spatiotemporal evolution of the traceless symmetric order parameter of a sheared nematogenic fluid. In particular we establish, by decisive numerical tests, that the irregular oscillatory behavior seen in a region of parameter space where the nematic is not stably flow-aligning is in fact spatiotemporal chaos. We outline the dynamical phase diagram of the model and study the route to the chaotic state. We find that spatiotemporal chaos in this system sets in via a regime of spatiotemporal intermittency, with a power-law distribution of the widths of laminar regions, as in H. Chate and P. Manneville, Phys. Rev. Lett. 58, 112 (1987). Further, the evolution of the histogram of band sizes shows a growing length scale as one moves from the chaotic towards the flow-aligned phase. Finally we suggest possible experiments in which one can observe the intriguing behaviors discussed here

A Rare Case of Cerebral Hemangioblastoma Mimicking as Anterior Choroid Plexus Cyst

Abstract A choroid plexus cyst may be present throughout the ventricular system of the brain. A hemangioblastoma is generally found in patients with genetic diseases like Von Hippel-Lindau (VHL) syndrome disease, but it can also be found sporadically in the spinal cord, retina and in rare cases in the cerebrum. An eighteen-year-old male subject was referred for autopsy in Kolkata police morgue on 27/02/2017. Two hours before, the patient had been brought to the hospital for severe headache; but before any diagnosis could be made, he collapsed and died. On autopsy, a 4cm fluid filled cyst was found in the anterior portion of third ventricle and sent for histopathological examination. HPE findings were consistent with a hemangioblastoma, which made this case extremely rare. Sudden death due to increased intracranial tension cases should be properly examined for any neuroepithelial tumours like a hemangioblastoma

The active site of a prototypical “rigid” drug target is marked by extensive conformational dynamics

Drug discovery, in particular optimization of candidates using medicinal chemistry, is generally guided by structural biology. However, for optimizing binding kinetics, relevant for efficacy and off-target effects, information on protein motion is important. Herein, we demonstrate for the prototypical textbook example of an allegedly “rigid protein” that substantial active-site dynamics have generally remained unrecognized, despite thousands of medicinal-chemistry studies on this model over decades. Comparing cryogenic X-ray structures, solid-state NMR on micro-crystalline protein at room temperature, and solution NMR structure and dynamics, supported by MD simulations, we show that under physiologically relevant conditions the pocket is in fact shaped by pronounced open/close conformational-exchange dynamics. The study, which is of general significance for pharmacological research, evinces a generic pitfall in drug discovery routines

Electron-Hole Asymmetry in the Electron-phonon Coupling in Top-gated Phosphorene Transistor

Using in-situ Raman scattering from phosphorene channel in an electrochemically top-gated field effect transistor, we show that its phonons with A$_g$ symmetry depend much more strongly on concentration of electrons than that of holes, while the phonons with B$_g$ symmetry are insensitive to doping. With first-principles theoretical analysis, we show that the observed electon-hole asymmetry arises from the radically different constitution of its conduction and valence bands involving $\pi$ and $\sigma$ bonding states respectively, whose symmetry permits coupling with only the phonons that preserve the lattice symmetry. Thus, Raman spectroscopy is a non-invasive tool for measuring electron concentration in phosphorene-based nanoelectronic devices

Spatiotemporal rheochaos in nematic hydrodynamics

Motivated by the observation of rheochaos in sheared wormlike micelles [Bandyopadhyay et al., Phys. Rev. Lett, 84 2022, (2000); Europhys. Lett. 56, 447 (2001); Pramana 53, 223 (1999)] we study the coupled nonlinear partial differential equations for the hydrodynamic velocity and order parameter fields in a sheared nematogenic fluid. In a suitable parameter range, we find irregular, dynamic shear-banding and establish by decisive numerical tests that the chaos we observe in the model is spatiotemporal in nature.Comment: Slight changes in text, references and Fig. 5 inset; 6 eps figures (figs 2,3,4 at lower resolution to reduce file size; full files available on request); accepted for publication in Phys Rev Let