2,153 research outputs found
The use of phenyl-Sepharose for the affinity purification of proteinases
Phenyl-Sepharose is most often used as an adsorbent for hydrophobic interaction chromatography (HIC). We report on its effective use for the affinity purification of some extracellular thermostable proteinases from bacterial sources. Proteinases belonging to the serine, aspartate and metallo mechanistic classes were effective retained by the media. Purification factors in the range of 2.9–60 and enzyme activity yields in excess of 88% were obtained. In some cases homogeneous enzyme was obtained from culture supernatants in a single step. A number of other proteinases from mammalian sources were also retained. The specificity of the enzyme/support interaction was studied. Proteinases complexed with peptide inhibitors (pepstatin and chymostatin) showed reduced binding to phenyl Sepharose indicating with the active site cleft whereas modification with low molecular weight active site directed inactivators such as PMSF and DAN did not, indicating that binding may not be dependent on the catalytic site. Pepsinogen and the pro-enzyme form of the serine proteinase from the thermophilic Bacillus sp. strain Ak.1 were not retained by the media and could be resolved in an efficient manner from their active counterparts
Measurement of optical to electrical and electrical to optical delays with ps-level uncertainty
We present a new measurement principle to determine the absolute time delay
of a waveform from an optical reference plane to an electrical reference plane
and vice versa. We demonstrate a method based on this principle with 2 ps
uncertainty. This method can be used to perform accurate time delay
determinations of optical transceivers used in fibre-optic time-dissemination
equipment. As a result the time scales in optical and electrical domain can be
related to each other with the same uncertainty. We expect this method to break
new grounds in high-accuracy time transfer and absolute calibration of
time-transfer equipment
Exploring the use of a web-based virtual patient to support learning through reflection
This thesis explores the support of learning through reflection, in the context of medical students and practitioners, working through a series of simulated consultations involving the diagnosis and management of chronic illness. A model of the medical consultative process was defined, on which a web-based patient simulation was developed. This simulation can be accessed over the Internet using commonly available web-browsers. It enables users to interact with a virtual patient by taking a history, examining the patient, requesting and reviewing investigations, and choosing appropriate management strategies. The virtual patient can be reviewed over a number of consultations, and the patient outcome is dependant on the management strategy selected by the user. A second model was also developed, that adds a layer of reflection over the consultative process. While interacting with the virtual patient users are asked to formulate and test their hypotheses. Simple tools are included to encourage users to record their observations and thoughts for further learning, as well as providing links to web-based library resources. At the end of each consultation, users are asked to review their actions and indicate whether they think their actions were critical, relevant, or not relevant to the diagnosis and management of the patient in light of their current knowledge. Users also have the opportunity to compare their activity to their peers or an expert in the case under study. Three formal cycles of evaluation were undertaken during the design and development of the software. A number of clinicians were involved in the initial design to ensure there was an appropriate structure that matched clinical practice. Formative evaluation was conducted to review the usability of the application, and based on user feedback a number of changes were made to the user interface and structure of the application. A third, end user, evaluation was undertaken using a single case concerning the diagnosis and management of hypertriglyceridaemia in the context of Type 1B Glycogen Storage Disease. This evaluation involved ten medical students, five general practitioners and two specialists. The evaluation involved observation using a simplified think-aloud, as well as administration of a questionnaire. Users were engaged by the simulation, and were able to use the application with only a short period of training. Usability issues still exist with respect to the processing of natural language input, especially when asking questions of the virtual patient. Until such time that natural language recognition is able to provide satisfactory performance, alternative, list-based, methods of interaction will be required. Evaluation involving medical students, general practitioners, and specialist medical practitioners demonstrated that reflection can be supported and encouraged by providing appropriate tools, as well as by judiciously interrupting the consultative process and providing time for reflection to take place. Reflection could have been further enhanced if users had been educated on reflection as a learning modality prior to using SIMPRAC. Further work is also required to improve the simulation environment, improve the interfaces for supporting reflection, and further define the benefits of using this approach for medical education and professional development with respect to learning outcomes and behavioural change
Reconstructing Deconstruction: High-Velocity Cloud Distance Through Disruption Morphology
We present Arecibo L-band Feed Array 21-cm observations of a sub-complex of
HVCs at the tip of the Anti-Center Complex. These observations show
morphological details that point to interaction with the ambient halo medium
and differential drag within the cloud sub-complex. We develop a new technique
for measuring cloud distances, which relies upon these observed morphological
and kinematic characteristics, and show that it is consistent with H-alpha
distances. These results are consistent with distances to HVCs and halo
densities derived from models in which HVCs are formed from cooling halo gas.Comment: 8 pages, 2 figures, 1 tabe, Accepted to Ap
Ongoing Galactic Accretion: Simulations and Observations of Condensed Gas in Hot Halos
Ongoing accretion onto galactic disks has been recently theorized to progress
via the unstable cooling of the baryonic halo into condensed clouds. These
clouds have been identified as analogous to the High-Velocity Clouds (HVCs)
observed in HI in our Galaxy. Here we compare the distribution of HVCs observed
around our own Galaxy and extra-planar gas around the Andromeda galaxy to these
possible HVC analogs in a simulation of galaxy formation that naturally
generates these condensed clouds. We find a very good correspondence between
these observations and the simulation, in terms of number, angular size,
velocity distribution, overall flux and flux distribution of the clouds. We
show that condensed cloud accretion only accounts for ~ 0.2 M_solar / year of
the current overall Galactic accretion in the simulations. We also find that
the simulated halo clouds accelerate and become more massive as they fall
toward the disk. The parameter space of the simulated clouds is consistent with
all of the observed HVC complexes that have distance constraints, except the
Magellanic Stream which is known to have a different origin. We also find that
nearly half of these simulated halo clouds would be indistinguishable from
lower-velocity gas and that this effect is strongest further from the disk of
the galaxy, thus indicating a possible missing population of HVCs. These
results indicate that the majority of HVCs are consistent with being infalling,
condensed clouds that are a remnant of Galaxy formation.Comment: 10 pages, 6 figures, ApJ Accepted. Some changes to techniqu
Measuring the 8621 \r{A} Diffuse Interstellar Band in Gaia DR3 RVS Spectra: Obtaining a Clean Catalog by Marginalizing over Stellar Types
Diffuse interstellar bands (DIBs) are broad absorption features associated
with interstellar dust and can serve as chemical and kinematic tracers.
Conventional measurements of DIBs in stellar spectra are complicated by
residuals between observations and best-fit stellar models. To overcome this,
we simultaneously model the spectrum as a combination of stellar, dust, and
residual components, with full posteriors on the joint distribution of the
components. This decomposition is obtained by modeling each component as a draw
from a high-dimensional Gaussian distribution in the data-space (the observed
spectrum) -- a method we call "Marginalized Analytic Data-space Gaussian
Inference for Component Separation" (MADGICS). We use a data-driven prior for
the stellar component, which avoids missing stellar features not well-modeled
by synthetic spectra. This technique provides statistically rigorous
uncertainties and detection thresholds, which are required to work in the low
signal-to-noise regime that is commonplace for dusty lines of sight. We
reprocess all public Gaia DR3 RVS spectra and present an improved 8621 \r{A}
DIB catalog, free of detectable stellar line contamination. We constrain the
rest-frame wavelength to \r{A} (vacuum), find no
significant evidence for DIBs in the Local Bubble from the of
RVS spectra that are public, and show unprecedented correlation with kinematic
substructure in Galactic CO maps. We validate the catalog, its reported
uncertainties, and biases using synthetic injection tests. We believe MADGICS
provides a viable path forward for large-scale spectral line measurements in
the presence of complex spectral contamination.Comment: 25 pages, 25 figures, submitted to Ap
Compact HI clouds from the GALFA-HI survey
The Galactic Arecibo L-band Feed Array HI (GALFA-HI) survey is mapping the
entire Arecibo sky at 21-cm, over a velocity range of -700 to +700 km/s (LSR),
at a velocity resolution of 0.18 km/s and a spatial resolution of 3.5 arcmin.
The unprecedented resolution and sensitivity of the GALFA-HI survey have
resulted in the detection of numerous isolated, very compact HI clouds at low
Galactic velocities, which are distinctly separated from the HI disk emission.
In the limited area of ~4600 deg surveyed so far, we have detected 96 of
such compact clouds. The detected clouds are cold with a median T
(the kinetic temperature in the case in which there is no non-thermal
broadening) of 300 K. Moreover, these clouds are quite compact and faint, with
median values of 5 arcmin in angular size, 0.75 K in peak brightness
temperature, and cm in HI column density. Most of the
clouds deviate from Galactic rotation at the 20-30 km/s level, and a
significant fraction show evidence for a multiphase medium and velocity
gradients. No counterparts for these clouds were found in other wavebands. From
the modeling of spatial and velocity distributions of the whole compact cloud
population, we find that the bulk of the compact clouds are related to the
Galactic disk, and their distances are likely to be in the range of 0.1 to a
few kpc. We discuss various possible scenarios for the formation and
maintenance of this cloud population and its significance for Galactic ISM
studies.Comment: Accepted for publication in the Astrophysical Journa
Multiphysics simulation of corona discharge induced ionic wind
Ionic wind devices or electrostatic fluid accelerators are becoming of
increasing interest as tools for thermal management, in particular for
semiconductor devices. In this work, we present a numerical model for
predicting the performance of such devices, whose main benefit is the ability
to accurately predict the amount of charge injected at the corona electrode.
Our multiphysics numerical model consists of a highly nonlinear strongly
coupled set of PDEs including the Navier-Stokes equations for fluid flow,
Poisson's equation for electrostatic potential, charge continuity and heat
transfer equations. To solve this system we employ a staggered solution
algorithm that generalizes Gummel's algorithm for charge transport in
semiconductors. Predictions of our simulations are validated by comparison with
experimental measurements and are shown to closely match. Finally, our
simulation tool is used to estimate the effectiveness of the design of an
electrohydrodynamic cooling apparatus for power electronics applications.Comment: 24 pages, 17 figure
The Effelsberg-Bonn HI Survey: Data reduction
Starting in winter 2008/2009 an L-band 7-Feed-Array receiver is used for a
21-cm line survey performed with the 100-m telescope, the Effelsberg-Bonn HI
survey (EBHIS). The EBHIS will cover the whole northern hemisphere for decl.>-5
deg comprising both the galactic and extragalactic sky out to a distance of
about 230 Mpc. Using state-of-the-art FPGA-based digital fast Fourier transform
spectrometers, superior in dynamic range and temporal resolution to
conventional correlators, allows us to apply sophisticated radio frequency
interference (RFI) mitigation schemes.
In this paper, the EBHIS data reduction package and first results are
presented. The reduction software consists of RFI detection schemes, flux and
gain-curve calibration, stray-radiation removal, baseline fitting, and finally
the gridding to produce data cubes. The whole software chain is successfully
tested using multi-feed data toward many smaller test fields (1--100 square
degrees) and recently applied for the first time to data of two large sky
areas, each covering about 2000 square degrees. The first large area is toward
the northern galactic pole and the second one toward the northern tip of the
Magellanic Leading Arm. Here, we demonstrate the data quality of EBHIS Milky
Way data and give a first impression on the first data release in 2011.Comment: 17 pages, 14 figures; to be published in ApJ
- …