627 research outputs found

### Calibration of Viking imaging system pointing, image extraction, and optical navigation measure

Pointing control and knowledge accuracy of Viking Orbiter science instruments is controlled by the scan platform. Calibration of the scan platform and the imaging system was accomplished through mathematical models. The calibration procedure and results obtained for the two Viking spacecraft are described. Included are both ground and in-flight scan platform calibrations, and the additional calibrations unique to optical navigation

### Mariner Mars 1971 optical navigation demonstration

The feasibility of using a combination of spacecraft-based optical data and earth-based Doppler data to perform near-real-time approach navigation was demonstrated by the Mariner Mars 71 Project. The important findings, conclusions, and recommendations are documented. A summary along with publications and papers giving additional details on the objectives of the demonstration are provided. Instrument calibration and performance as well as navigation and science results are reported

### Comments on Black Holes in Matrix Theory

The recent suggestion that the entropy of Schwarzschild black holes can be
computed in matrix theory using near-extremal D-brane thermodynamics is
examined. It is found that the regime in which this approach is valid actually
describes black strings stretched across the longitudinal direction, near the
transition where black strings become unstable to the formation of black holes.
It is argued that the appropriate dynamics on the other (black hole) side of
the transition is that of the zero modes of the corresponding super Yang-Mills
theory. A suggestive mean field theory argument is given for the entropy of
black holes in all dimensions. Consequences of the analysis for matrix theory
and the holographic principle are discussed.Comment: 15 pages, harvmac, minor errors correcte

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### Bearing witness and being bounded; the experiences of nurses in adult critical care in relation to the survivorship needs of patients and families

Aim: To discern and understand the responses of nurses to the survivorship needs of patients and family members in adult critical care units.
Background: The critical care environment is a demanding place of work which may limit nurses to immediacy of care, such is the proximity to death and the pressure of work.
Design: A constructivist grounded theory approach with constant comparative analysis.
Methods: As part of a wider study and following ethical approval, eleven critical care nurses working within a general adult critical care unit were interviewed with respect to their experiences in meeting the psychosocial needs of patients and family members. Through the process of constant comparative analysis an overarching selective code was constructed. EQUATOR guidelines for qualitative research (COREQ) applied.
Results: The data illuminated a path of developing expertise permitting integration of physical, psychological and family care with technology and humanity. Gaining such proficiency is demanding and the data presented reveals the challenges that nurses experience along the way.
Conclusion: The study confirms that working within a critical care environment is an emotionally charged challenge and may incur an emotional cost. Nurses can find themselves bounded by the walls of the critical care unit and experience personal and professional conflicts in their role. Nurses bear witness to the early stages of the survivorship trajectory but are limited in their support of ongoing needs.
Relevance to Clinical Practice: Critical care nurses can experience personal and professional conflicts when caring for both patients and families. This can lead to moral distress and may contribute to compassion fatigue. Critical care nurses appear bounded to the delivery of physiological and technical care, in the moment, as demanded by the patient's acuity. Consequentially this limits nursesâ€™ ability to support the onward survivorship trajectory. Increased pressure and demands on critical care beds has contributed further to occupational stress in this care setting

### General Rotating Black Holes in String Theory: Greybody Factors and Event Horizons

We derive the wave equation for a minimally coupled scalar field in the
background of a general rotating five-dimensional black hole. It is written in
a form that involves two types of thermodynamic variables, defined at the inner
and outer event horizon, respectively. We model the microscopic structure as an
effective string theory, with the thermodynamic properties of the left and
right moving excitations related to those of the horizons. Previously known
solutions to the wave equation are generalized to the rotating case, and their
regime of validity is sharpened. We calculate the greybody factors and
interpret the resulting Hawking emission spectrum microscopically in several
limits. We find a U-duality invariant expression for the effective string
length that does not assume a hierarchy between the charges. It accounts for
the universal low-energy absorption cross-section in the general non-extremal
case.Comment: 33 pages, latex; minor typos corrected; version to appear in PR

### A surprisingly simple electrostatic model explains bent vs. linear structures in M+-RG2 species (M = group 1 metal, Liâ€“Fr; RG = rare gas, Heâ€“Rn)

It is found that a simple electrostatic model involving competition between the attractive dispersive interaction and induced-dipole repulsion between the two RG atoms performs extremely well in rationalizing the M+-RG2 geometries, where M = Group 1 metal and RG = rare gas. The Li+-RG2 and Na+-RG2 complexes have previously been found to exhibit quasilinear or linear minimum energy geometries, with the Na+-RG2 complexes having an additional bent local minimum [A. Andrejeva, A. M. Gardner, J. B. Graneek, R. J. Plowright, W. H. Breckenridge and T. G. Wright, J. Phys. Chem. A, 2013, 117, 13578]. In the present work, the geometries for M = Kâ€“Fr are found to be bent. A simple electrostatic model explains these conclusions and is able to account almost quantitatively for the binding energy of the second RG atom, as well as the form of the angular potential, for all thirty six titular species. Additionally, results of population analyses are presented together with orbital contour plots; combined with the success of the electrostatic model, the expectation that these complexes are all physically bound is confirmed

### Can the effective string see higher partial waves?

The semi-classical cross-sections for arbitrary partial waves of ordinary
scalars to fall into certain five-dimensional black holes have a form that
seems capable of explanation in terms of the effective string model. The
kinematics of these processes is analyzed in detail on the effective string and
is shown to reproduce the correct functional form of the semi-classical
cross-sections. But it is necessary to choose a peculiar value of the effective
string tension to obtain the correct scaling properties. Furthermore, the
assumptions of locality and statistics combine to forbid the effective string
from absorbing more than a finite number of partial waves. The relation of this
limitation to cosmic censorship is discussed.Comment: 19 pages, uses harvmac, version to appear in Phys. Rev.

### Effective spatial dimension of extremal non-dilatonic black p-branes and the description of entropy on the world volume

By investigating the critical behavior appearing at the extremal limit of the
non-dilatonic, black p-branes in (d+p) dimensions, we find that some critical
exponents related to the critical point obey the scaling laws. From the scaling
laws we obtain that the effective spatial dimension of the non-dilatonic black
holes and black strings is one, and is p for the non-dilatonic black p-branes.
For the dilatonic black holes and black p-branes, the effective dimension will
depend on the parameters in theories. Thus, we give an interpretation why the
Bekenstein-Hawking entropy may be given a simple world volume interpretation
only for the non-dilatonic black p-branes.Comment: 4 pages, RevTex, no figures, to appear in Phys. Rev. Let

### Supertubes

It is shown that a IIA superstring carrying D0-brane charge can be
`blown-up', in a {\it Minkowski vacuum} background, to a (1/4)-supersymmetric
tubular D2-brane, supported against collapse by the angular momentum generated
by crossed electric and magnetic Born-Infeld fields. This `supertube' can be
viewed as a worldvolume realization of the sigma-model Q-lump.Comment: Revision includes mention of some configurations dual to the
supertub

### D-branes and Near Extremal Black Holes at Low Energies

It has been observed recently that many properties of some near extremal
black holes can be described in terms of bound states of D-branes. Using a
non-renormalization theorem we argue that the D-brane description is the
correct quantum gravity description of the black hole at low energies. The low
energy theory includes the black hole degrees of freedom that account for the
entropy and describes also Hawking radiation. The description is unitary and
there seems to be no information loss at low energies.Comment: 14 pages, 2 figures, uses harvmac, an error in a proof is corrected,
the conclusions are the sam

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