380 research outputs found
Kathetergestützte Aortenklappenimplantation: Was müssen Anästhesisten wissen?
Zusammenfassung: Der chirurgische Aortenklappenersatz gilt als Goldstandard in der Therapie der hochgradigen Aortenklappenstenose. Die veränderte Demografie konfrontiert die behandelnden medizinischen Fachdisziplinen jedoch mit einem zunehmend höheren Risikoprofil der Patienten; dies machte die Entwicklung neuer weniger invasiver Behandlungsalternativen in der operativen Therapie der Aortenklappenstenose erforderlich. Dieser Entwicklungsprozess führte über die Minithorakotomie hin zur kathetergestützten Aortenklappenimplantation ("transcatheter aortic valve implantation", TAVI). Die TAVI ist ein neues therapeutisches Verfahren zur Behandlung von Patienten mit hochgradiger Aortenklappenstenose und hohem perioperativen Morbiditäts- sowie Mortalitätsrisiko für einen konventionellen Aortenklappenersatz. Da die TAVI am schlagenden Herzen ohne Sternotomie und Herz-Lungen-Maschine durchgeführt werden kann, eignet sich dieses Verfahren insbesondere für den älteren, multimorbiden und/oder kardial voroperierten Patienten. Die ersten Ergebnisse großer prospektiver Multizenterstudien unterstreichen den Stellenwert der TAVI in der modernen Behandlung von Hochrisikopatienten mit symptomatischer Aortenklappenstenose. Die TAVI erfordert vom Anästhesisten neben dem Verständnis des chirurgischen Ablaufs die genaue Kenntnis des perioperativen anästhesiologischen Managements und der möglichen Komplikationen des Verfahren
Modeling the Void H I Column Density Spectrum
The equivalent width distribution function (EWDF) of \hone absorbers specific
to the void environment has been recently derived (Manning 2002), revealing a
large line density of clouds (dN/dz ~500 per unit z for Log (N_HI)> 12.4). I
show that the void absorbers cannot be diffuse (or so-called filamentary)
clouds, expanding with the Hubble flow, as suggested by N-body/hydro
simulations. Absorbers are here modeled as the baryonic remnants of
sub-galactic perturbations that have expanded away from their dark halos in
response to reionization at z ~ 6.5. A 1-D Lagrangian hydro/gravity code is
used to follow the dynamic evolution and ionization structure of the baryonic
clouds for a range of halo circular velocities. The simulation products at z=0
can be combined according to various models of the halo velocity distribution
function to form a column density spectrum that can be compared with the
observed. I find that such clouds may explain the observed EWDF if the halo
velocity distribution function is as steep as that advanced by Klypin (1999),
and the halo mass distribution is closer to isothermal than to NFW.Comment: 21 pages, 15 figures. Paper in press; ApJ 591, n
Correlation between the Mean Matter Density and the Width of the Saturated Lyman Alpha Absorption
We report a scaling of the mean matter density with the width of the
saturated Lyman alpha absorptions. This property is established using the
``pseudo-hydro'' technique (Croft et al. 1998). It provides a constraint for
the inversion of the Lyman alpha forest, which encounters difficulty in the
saturated region. With a Gaussian density profile and the scaling relation, a
simple inversion of the simulated Lyman alpha forests shows that the
one-dimensional mass power spectrum is well recovered on scales above 2 Mpc/h,
or roughly k < 0.03 s/km, at z=3. The recovery underestimates the power on
small scales, but improvement is possible with a more sophisticated algorithm.Comment: 7 pages, 9 figures, accepted for publication in MNRAS, replaced by
the version after proo
The Relationship Between Galaxies and Low Redshift Weak Lyman alpha Absorbers in the Directions of H1821+643 and PG1116+215
To study the nature of low z Lya absorbers in the spectra of QSOs, we have
obtained high signal-to-noise UV spectra of H 1821+643 (z = 0.297) and PG
1116+215 (z = 0.177) with the GHRS on the HST. The spectra have minimum S/N of
70-100 and 3 sigma limiting equivalent widths of 50-75 mA. We detect 26 Lya
lines with Wr > 50 mA toward H1821+643 and 13 toward PG1116+215, which implies
a density of 102+/-16 lines per unit redshift. The two-point correlation
function shows marginal evidence of clustering on ~500 km/s scales, but only if
the weakest lines are excluded. We have also used the WIYN Observatory to
measure galaxy redshifts in the ~1 degree fields centered on each QSO. We find
17 galaxy-absorber pairs within projected distances of 1 Mpc with velocity
separations of 350 km/s or less. Monte Carlo simulations show that if the Lya
lines are randomly distributed, the probability of observing this many close
pairs is 3.6e-5. We find that all galaxies with projected distances of 600 kpc
or less have associated Lya absorbers within 1000 km/s, and the majority of
these galaxies have absorbers within 350 km/s. We also find that the Lya
equivalent width is anticorrelated with the projected distance of the nearest
galaxy out to at least 600 kpc, but this should be interpreted cautiously
because there are potential selection biases. Statistical tests using the
entire sample also indicate that the absorbers are not randomly distributed. We
discuss the nature of the Lya absorbers in light of the new data.Comment: Accepted for publication in ApJ. 17 pages plus 11 tables and 17
figure
The Search for Intergalactic Hydrogen Clouds in Voids
I present the results of a search for intergalactic hydrogen clouds in voids.
Clouds are detected by their HI LyA absorption lines in the HST spectra of
low-redshift AGN. The parameter with which the environments of clouds are
characterized is the tidal field, which places a lower limit on the cloud
mass-density which is dynamically stable against disruption. Galaxy redshift
catalogs are used to sum the tidal fields along the lines of sight, sorting
clouds according to tidal field upper, or lower limits. The analytical
methodology employed is designed to detect gas clouds whose expansion following
reionization is restrained by dark matter perturbations. End-products are the
cloud equivalent width distribution functions (EWDF) of catalogs formed by
sorting clouds according to various tidal field upper, or lower limits.
Cumulative EWDFs are steep in voids (S ~ -1.5 \pm 0.2), but flatter in high
tidal field zones (S ~ -0.5 \pm 0.1). Most probable cloud Doppler parameters
are ~30 km/s in voids and ~60 km/s in proximity to galaxies. In voids, the
cumulative line density at low EW (~ 15 mA) is ~ 500 per unit redshift. The
void filling factor is found to be 0.87 <= f_v <= 0.94. The void EWDF is
remarkably uniform over this volume, with a possible tendency for more massive
clouds to be in void centers. The size and nature of the void cloud population
suggested by this study is completely unanticipated by the results of published
3-D simulations, which predict that most clouds are in filamentary structures
around galaxy concentrations, and that very few observable absorbers would lie
in voids. Strategies for modeling this population are briefly discussed.Comment: 21 pages, 19 figures, apjemulate style, to appear in ApJ vol. 57
The Nature and Origin of the Non-Void Lyman alpha Cloud Population
I continue my study of the low-z Lyman alpha cloud population. Previously I
showed how galaxy catalogs are used to attribute relative degrees of isolation
to those clouds found in HST/GHRS spectra. I find that there exist two distinct
populations corresponding to two distinct environments, variously characterized
as void (unshocked) and non-void (shocked). Void clouds have a steep equivalent
width distribution (i.e., many smaller absorbers) while non-void clouds have a
flat distribution. These environment-specific observations of LyA clouds show
that the predictions from N-body/hydro simulations are incorrect. Simulations
fail to predict the existence of significant numbers of detectable void clouds.
They incorrectly predict the characteristics of non-void clouds. Implicated in
this failure is the so-called fluctuating Gunn-Peterson Approximation (FGPA)
which envisions that LyA absorbers are formed in the large-scale structures of
coalescing matter. I recently modeled the void cloud population as sub-galactic
perturbations that have expanded in response to reionization. However, the
success in this modeling was contingent upon using the more massive isothermal
halo in place of the standard Navarro, Frenk & White. Here, I extend my
modeling to non-void LyA clouds using the same basic cloud model. Nonvoid
clouds were once unshocked, but when entering nonvoid space, they are shock
stripped. By analytically stripping model void clouds, a good fit of the model
CDS to observations is found if cloud velocities are ~100 km/s. Nonvoid clouds
show strong concentration around galaxies, suggesting that the compact HVC
population are members of this population.Comment: 10 pages, 6 figures, ApJ 595 n1, in pres
A semi-automated BPMN-based framework for detecting conflicts between security, data-minimization, and fairness requirements
Requirements are inherently prone to conflicts. Security, data-minimization, and fairness requirements are no exception. Importantly, undetected conflicts between such requirements can lead to severe effects, including privacy infringement and legal sanctions. Detecting conflicts between security, data-minimization, and fairness requirements is a challenging task, as such conflicts are context-specific and their detection requires a thorough understanding of the underlying business processes. For example, a process may require anonymous execution of a task that writes data into a secure data storage, where the identity of the writer is needed for the purpose of accountability. Moreover, conflicts not arise from trade-offs between requirements elicited from the stakeholders, but also from misinterpretation of elicited requirements while implementing them in business processes, leading to a non-alignment between the data subjects’ requirements and their specifications. Both types of conflicts are substantial challenges for conflict detection. To address these challenges, we propose a BPMN-based framework that supports: (i) the design of business processes considering security, data-minimization and fairness requirements, (ii) the encoding of such requirements as reusable, domain-specific patterns, (iii) the checking of alignment between the encoded requirements and annotated BPMN models based on these patterns, and (iv) the detection of conflicts between the specified requirements in the BPMN models based on a catalog of domain-independent anti-patterns. The security requirements were reused from SecBPMN2, a security-oriented BPMN 2.0 extension, while the fairness and data-minimization parts are new. For formulating our patterns and anti-patterns, we extended a graphical query language called SecBPMN2-Q. We report on the feasibility and the usability of our approach based on a case study featuring a healthcare management system, and an experimental user study. \ua9 2020, The Author(s)
Discovery of a z=4.93, X-ray selected quasar by the Chandra Multiwavelength Project (ChamP)
We present X-ray and optical observations of CXOMP J213945.0-234655, a high
redshift (z=4.93) quasar discovered through the Chandra Multiwavelength Project
(ChaMP). This object is the most distant X-ray selected quasar published, with
an X-ray luminosity of L(X)=5.9x10^44 erg/s (measured in the 0.3-2.5 keV band
and corrected for Galactic absorption). CXOMP J213945.0-234655 is a g' dropout
object (>26.2), with r'=22.87 and i'=21.36. The rest-frame X-ray to optical
flux ratio is similar to quasars at lower redshifts and slightly X-ray bright
relative to z>4 optically-selected quasars observed with Chandra. The ChaMP is
beginning to acquire significant numbers of high redshift quasars to
investigate the unobscured X-ray luminosity function out to z~5.Comment: Published in ApJ Letters; 4 pages; 3 figures;
http://hea-www.harvard.edu/CHAMP
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