Remote water monitoring system

A remote water monitoring system is described that integrates the functions of sampling, sample preservation, sample analysis, data transmission and remote operation. The system employs a floating buoy carrying an antenna connected by lines to one or more sampling units containing several sample chambers. Receipt of a command signal actuates a solenoid to open an intake valve outward from the sampling unit and communicates the water sample to an identifiable sample chamber. Such response to each signal receipt is repeated until all sample chambers are filled in a sample unit. Each sample taken is analyzed by an electrochemical sensor for a specific property and the data obtained is transmitted to a remote sending and receiving station. Thereafter, the samples remain isolated in the sample chambers until the sampling unit is recovered and the samples removed for further laboratory analysis

Tidal Effects in Clusters of Galaxies

High-redshift clusters of galaxies show an over-abundance of spirals by a factor of 2-3, and the corresponding under-abundance of S0 galaxies, relative to the nearby clusters. This morphological evolution can be explained by tidal interactions with neighboring galaxies and with the hierarchically growing cluster halo. The efficiency of tidal interactions depends on the size and structure of the cluster, as well as on the epoch of its formation. I simulate the formation and evolution of Virgo-type clusters in three cosmologies: a critical density model Omega_0=1, an open model Omega_0=0.4, and a flat model Omega_0=0.4 with a cosmological constant. The orbits of identified halos are traced with a high temporal resolution (~10^7 yr). Halos with low relative velocities merge only shortly after entering the cluster; after virialization mergers are suppressed. The dynamical evolution of galaxies is determined by the tidal field along their trajectories. The maxima of the tidal force do not always correspond to closest approach to the cluster center. They are produced to a large extent by the local density structures, such as the massive galaxies and the unvirialized remnants of infalling groups of galaxies. Collisions of galaxies are intensified by the substructure, with about 10 encounters within 10 kpc per galaxy in the Hubble time. These very close encounters add an important amount (10-50%) of the total heating rate. The integrated effect of tidal interactions is insufficient to transform a spiral galaxy into an elliptical, but can produce an S0 galaxy. Overall, tidal heating is stronger in the low Omega_0 clusters

Sense and specificity in neuronal calcium signalling

AbstractChanges in the intracellular free calcium concentration ([Ca2+]i) in neurons regulate many and varied aspects of neuronal function over time scales from microseconds to days. The mystery is how a single signalling ion can lead to such diverse and specific changes in cell function. This is partly due to aspects of the Ca2+ signal itself, including its magnitude, duration, localisation and persistent or oscillatory nature. The transduction of the Ca2+ signal requires Ca2+ binding to various Ca2+ sensor proteins. The different properties of these sensors are important for differential signal processing and determine the physiological specificity of Ca2+ signalling pathways. A major factor underlying the specific roles of particular Ca2+ sensor proteins is the nature of their interaction with target proteins and how this mediates unique patterns of regulation. We review here recent progress from structural analyses and from functional analyses in model organisms that have begun to reveal the rules that underlie Ca2+ sensor protein specificity for target interaction. We discuss three case studies exemplifying different aspects of Ca2+ sensor/target interaction. This article is part of a special issue titled the 13th European Symposium on Calcium

Electrostatic considerations affecting the calculated HOMO-LUMO gap in protein molecules.

A detailed study of energy differences between the highest occupied and lowest unoccupied molecular orbitals (HOMO-LUMO gaps) in protein systems and water clusters is presented. Recent work questioning the applicability of Kohn-Sham density-functional theory to proteins and large water clusters (E. Rudberg, J. Phys.: Condens. Mat. 2012, 24, 072202) has demonstrated vanishing HOMO-LUMO gaps for these systems, which is generally attributed to the treatment of exchange in the functional used. The present work shows that the vanishing gap is, in fact, an electrostatic artefact of the method used to prepare the system. Practical solutions for ensuring the gap is maintained when the system size is increased are demonstrated. This work has important implications for the use of large-scale density-functional theory in biomolecular systems, particularly in the simulation of photoemission, optical absorption and electronic transport, all of which depend critically on differences between energies of molecular orbitals.Comment: 13 pages, 4 figure

NGC 4254: An Act of Harassment Uncovered by the Arecibo Legacy Fast ALFA Survey

We present an HI map constructed from the Arecibo Legacy Fast ALFA (ALFALFA) survey of the surroundings of the strongly asymmetric Virgo cluster Sc galaxy NGC 4254. Noted previously for its lopsided appearance, rich interstellar medium, and extradisk HI emission, NGC 4254 is believed to be entering the Virgo environment for the first time and at high speed. The ALFALFA map clearly shows a long HI tail extending ~250 kpc northward from the galaxy. Embedded as one condensation within this HI structure is the object previously identified as a "dark galaxy": Virgo HI21 (Davies et al. 2004). A body of evidence including its location within and velocity with respect to the cluster and the appearance and kinematics of its strong spiral pattern, extra-disk HI and lengthy HI tail is consistent with a picture of "galaxy harassment" as proposed by Moore et al. (1996a,b; 1998). The smoothly varying radial velocity field along the tail as it emerges from NGC 4254 can be used as a timing tool, if interpreted as resulting from the coupling of the rotation of the disk and the collective gravitational forces associated with the harassment mechanism.Comment: accepted for publication in Ap.J.(Lett.). higher resolution figure available at http://egg.astro.cornell.edu/alfalfa/pubs/figs/n4254_f1.ep

Predicting solvatochromic shifts and colours of a solvated organic dye: the example of nile red

The solvatochromic shift, as well as the change in colour of the simple organic dye nile red, is studied in two polar and two non-polar solvents in the context of large-scale time-dependent density-functional theory (TDDFT) calculations treating large parts of the solvent environment from first principles. We show that an explicit solvent representation is vital to resolve absorption peak shifts between nile red in n-hexane and toluene, as well as acetone and ethanol. The origin of the failure of implicit solvent models for these solvents is identified as being due to the strong solute-solvent interactions in form of π-stacking and hydrogen bonding in the case of toluene and ethanol. We furthermore demonstrate that the failures of the computationally inexpensive Perdew-Burke-Ernzerhof (PBE) functional in describing some features of the excited state potential energy surface of the S1 state of nile red can be corrected for in a straightforward fashion, relying only on a small number of calculations making use of more sophisticated range-separated hybrid functionals. The resulting solvatochromic shifts and predicted colours are in excellent agreement with experiment, showing the computational approach outlined in this work to yield very robust predictions of optical properties of dyes in solution

Neuronal calcium sensor proteins: emerging roles in membrane traffic and synaptic plasticity

Ca2+ plays a crucial role in the regulation of neuronal function. Recent work has revealed important functions for two families of neuronally expressed Ca2+ sensor proteins. These include roles in membrane traffic and in alterations in synaptic plasticity underlying changes in behaviour