4,088 research outputs found
Considering the impact of situation-specific motivations and constraints in the design of naturally ventilated and hybrid buildings
A simple logical model of the interaction between a building and its occupants is presented based on the principle that if free to do so, people will adjust their posture, clothing or available building controls (windows, blinds, doors, fans, and thermostats) with the aim of achieving or restoring comfort and reducing discomfort. These adjustments are related to building design in two ways: first the freedom to adjust depends on the availability and ease-of-use of control options; second the use of controls affects building comfort and energy performance. Hence it is essential that these interactions are considered in the design process. The model captures occupant use of controls in response to thermal stimuli (too warm, too cold etc.) and non-thermal stimuli (e.g. desire for fresh air). The situation-specific motivations and constraints on control use are represented through trigger temperatures at which control actions occur, motivations are included as negative constraints and incorporated into a single constraint value describing the specifics of each situation. The values of constraints are quantified for a range of existing buildings in Europe and Pakistan. The integration of the model within a design flow is proposed and the impact of different levels of constraints demonstrated. It is proposed that to minimise energy use and maximise comfort in naturally ventilated and hybrid buildings the designer should take the following steps: 1. Provide unconstrained low energy adaptive control options where possible, 2. Avoid problems with indoor air quality which provide motivations for excessive ventilation rates, 3. Incorporate situation-specific adaptive behaviour of occupants in design simulations, 4. Analyse the robustness of designs against variations in patterns of use and climate, and 5. Incorporate appropriate comfort standards into the operational building controls (e.g. BEMS)
The Asymmetric Thick Disk: A Star Count and Kinematic Analysis. II The Kinematics
We report a kinematic signature associated with the observed asymmetry in the
distribution of thick disk/inner halo stars interior to the Solar circle
described in Paper I. In that paper we found a statistically significant excess
(20% to 25 %) of stars in quadrant I (l ~ 20 deg to 55 deg) both above and
below the plane (b ~ +/- 25 deg to +/- 45 deg) compared to the complementary
region in quadrant IV. We have measured Doppler velocities for 741 stars,
selected according to the same magnitude and color criteria, in the direction
of the asymmetry and in the corresponding fields in quadrant IV. We have also
determined spectral types and metallicities measured from the same spectra. We
not only find an asymmetric distribution in the V_LSR velocities for the stars
in the two regions, but the angular rate of rotation, w, for the stars in
quadrant I reveals a slower effective rotation rate compared to the
corresponding quadrant IV stars. We use our [Fe/H] measurements to separate the
stars into the three primary population groups, halo, thick disk, and disk, and
conclude that it is primarily the thick disk stars that show the slower
rotation in quadrant I. A solution for the radial, tangential and vertical
components of the V_LSR velocities, reveals a significant lag of ~ 80 to 90
km/s in the direction of Galactic rotation for the thick disk stars in quadrant
I, while in quadrant IV, the same population has only a ~ 20 km/s lag. The
results reported here support a rotational lag among the thick disk stars due
to a gravitational interaction with the bar as the most likely explanation for
the asymmetry in both the star counts and the kinematics. The affected thick
disk stars, however, may be associated with the recently discovered Canis Major
debris stream or a similar merger event (abridged).Comment: Accepted for publication in the Astronomical Journa
On two theorems for flat, affine group schemes over a discrete valuation ring
We include short and elementary proofs of two theorems characterizing
reductive group schemes over a discrete valuation ring, in a slightly more
general context.Comment: 10 pages. To appear in C. E. J.
Two New LBV Candidates in the M33 Galaxy
We present two new luminous blue variable (LBV) candidate stars discovered in
the M33 galaxy. We identified these stars (Valeev et al. 2010) as massive star
candidates at the final stages of evolution, presumably with a notable
interstellar extinction. The candidates were selected from the Massey et al.
(2006) catalog based on the following criteria: emission in Halpha, V<18.5 and
0.35<(B-V)<1.2. The spectra of both stars reveal a broad and strong Halpha
emission with extended wings (770 and 1000 km/s). Based on the spectra we
estimated the main parameters of the stars. Object N45901 has a bolometric
luminosity log(L/Lsun)=6.0-6.2 with the value of interstellar extinction
Av=2.3+-0.1. The temperature of the star's photosphere is estimated as
Tstar~13000-15000K its probable mass on the Zero Age Main Sequence is
M~60-80Msun. The infrared excess in N45901 corresponds to the emission of warm
dust with the temperature Twarm~1000K, and amounts to 0.1% of the bolometric
luminosity. A comparison of stellar magnitude estimates from different catalogs
points to the probable variability of the object N45901. Bolometric luminosity
of the second object, N125093, is log(L/Lsun)=6.3-6.6, the value of
interstellar extinction is Av=2.75+-0.15. We estimate its photosphere's
temperature as Tstar~13000-16000K, the initial mass as M~90-120Msun. The
infrared excess in N125093 amounts to 5-6% of the bolometric luminosity. Its
spectral energy distribution reveals two thermal components with the
temperatures Twarm~1000K and Tcold~480K. The [CaII] lines (7291A and 7323A),
observed in LBV-like stars VarA and N93351 in M33, are also present in the
spectrum of N125093. These lines indicate relatively recent gas eruptions and
dust activity linked with them. High bolometric luminosity of these stars and
broad Halpha emissions allow classifying the studied objects as LBV candidates.Comment: 14 pages, 4 figure
Matching Spherical Dust Solutions to Construct Cosmological Models
Conditions for smooth cosmological models are set out and applied to
inhomogeneous spherically symmetric models constructed by matching together
different Lemaitre-Tolman-Bondi solutions to the
Einstein field equations. As an illustration the methods are applied to a
collapsing dust sphere in a curved background. This describes a region which
expands and then collapses to form a black hole in an
Einstein de Sitter background. We show that in all such models if there is no
vacuum region then the singularity must go on accreting matter for an infinite
LTB time.Comment: 13 pages, Revtex; to appear Gen. Rel. Gra
Strongly star-forming rotating disks in a complex merging system at z = 4,7 as revealed by ALMA
We performed a kinematical analysis of the [CII] line emission of the BR
1202-0725 system at z~4,7 using ALMA observations. The most prominent sources
of this system are a quasar and a submillimeter galaxy, separated by a
projected distance of about 24 kpc and characterized by very high SFR, higher
than 1000 Msun/yr. However, the ALMA observations reveal that these galaxies
apparently have undisturbed rotating disks, which is at variance with the
commonly accepted scenario in which strong star formation activity is induced
by a major merger. We also detected faint components which, after spectral
deblending, were spatially resolved from the main QSO and SMG emissions. The
relative velocities and positions of these components are compatible with
orbital motions within the gravitational potentials generated by the QSO host
galaxy and the SMG, suggesting that they are smaller galaxies in interaction or
gas clouds in accretion flows of tidal streams. We did not find any clear
spectral evidence for outflows caused by AGN or stellar feedback. This suggests
that the high star formation rates might be induced by interactions or minor
mergers with these companions, which do not affect the large-scale kinematics
of the disks, however. Our kinematical analysis also indicates that the QSO and
the SMG have similar Mdyn, mostly in the form of molecular gas, and that the
QSO host galaxy and the SMG are seen close to face-on with slightly different
disk inclinations: the QSO host galaxy is seen almost face-on (i~15), while the
SMG is seen at higher inclinations (i~25). Finally, the ratio between the black
hole mass of the QSO, obtained from XShooter spectroscopy, and the Mdyn of the
host galaxy is similar to value found in very massive local galaxies,
suggesting that the evolution of black hole galaxy relations is probably better
studied with dynamical than with stellar host galaxy masses.Comment: Accepted for publication in Astronomy and Astrophysic
Non-crystallographic reduction of generalized Calogero-Moser models
We apply a recently introduced reduction procedure based on the embedding of non-crystallographic Coxeter groups into crystallographic ones to CalogeroâMoser systems. For rational potentials the familiar generalized Calogero Hamiltonian is recovered. For the Hamiltonians of trigonometric, hyperbolic and elliptic types, we obtain novel integrable dynamical systems with a second potential term which is rescaled by the golden ratio. We explicitly show for the simplest of these non-crystallographic models, how the corresponding classical equations of motion can be derived from a Lie algebraic Lax pair based on the larger, crystallographic Coxeter group
Shrinking II -- The Distortion of the Area Distance-Redshift Relation in Inhomogeneous Isotropic Universes
This paper and the others in the series challenge the standard model of the
effects of gravitational lensing on observations at large distances. We show
that due to the cumulative effect of lensing, areas corresponding to an
observed solid angle can be quite different than would be estimated from the
corresponding Friedmann-Lema\^{\i}tre model, even when averaged over large
angular scales. This paper concentrates on the specific example of spherically
symmetric but spatially inhomogeneous dust universes, the
Lema\^{\i}tre-Tolman-Bondi models, and shows that radial lensing significantly
distorts the area distance-redshift and density-redshift relations in these
exact solutions compared with the standard ones for Friedmann-Lema\^{\i}tre
models. Thus inhomogeneity may introduce significant errors into distance
estimates based on the standard FL relations, even after all-sky averaging. In
addition a useful new gauge choice is presented for these models, solving the
problem of locating the past null cone exactly.Comment: Minor technical refinement, 16 pages, RevTex, 8 eps figure
Disk winds of B[e] supergiants
The class of B[e] supergiants is characterized by a two-component stellar
wind consisting of a normal hot star wind in the polar zone and a slow and
dense disk-like wind in the equatorial region. The properties of the disk wind
are discussed using satellite UV spectra of stars seen edge-on, i.e. through
the equatorial disk. These observations show that the disk winds are extremely
slow, 50-90 km/s, i.e. a factor of about 10 slower than expected from the
spectral types. Optical emission lines provide a further means to study the
disk wind. This is discussed for line profiles of forbidden lines formed in the
disk.Comment: 7 pages, LaTeX, 3 ps figures, uses lamuphys.sty from Springer-Verlag,
to be published in the proceedings of IAU Coll. 169 "Variable and
Non-spherical Stellar Winds in Luminous Hot Stars" held in Heidelberg 199
Free Fermionic Heterotic Model Building and Root Systems
We consider an alternative derivation of the GSO Projection in the free
fermionic construction of the weakly coupled heterotic string in terms of root
systems, as well as the interpretation of the GSO Projection in this picture.
We then present an algorithm to systematically and efficiently generate input
sets (i.e. basis vectors) in order to study Landscape statistics with minimal
computational cost. For example, the improvement at order 6 is approximately
10^{-13} over a traditional brute force approach, and improvement increases
with order. We then consider an example of statistics on a relatively simple
class of models.Comment: Standard Latex, 12 page
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