1,074 research outputs found
Non-analytic microscopic phase transitions and temperature oscillations in the microcanonical ensemble: An exactly solvable 1d-model for evaporation
We calculate exactly both the microcanonical and canonical thermodynamic
functions (TDFs) for a one-dimensional model system with piecewise constant
Lennard-Jones type pair interactions. In the case of an isolated -particle
system, the microcanonical TDFs exhibit (N-1) singular (non-analytic)
microscopic phase transitions of the formal order N/2, separating N
energetically different evaporation (dissociation) states. In a suitably
designed evaporation experiment, these types of phase transitions should
manifest themselves in the form of pressure and temperature oscillations,
indicating cooling by evaporation. In the presence of a heat bath (thermostat),
such oscillations are absent, but the canonical heat capacity shows a
characteristic peak, indicating the temperature-induced dissociation of the
one-dimensional chain. The distribution of complex zeros (DOZ) of the canonical
partition may be used to identify different degrees of dissociation in the
canonical ensemble.Comment: version accepted for publication in PRE, minor additions in the text,
references adde
Evidence for mid-Holocene rice domestication in the Americas
This is the author accepted manuscript. The final version is available from Springer Nature via the DOI in this recordThe development of agriculture is one of humankind's most pivotal achievements. Questions about plant domestication and the origins of agriculture have engaged scholars for well over a century, with implications for understanding its legacy on global subsistence strategies, plant distribution, population health and the global methane budget. Rice is one of the most important crops to be domesticated globally, with both Asia (Oryza sativa L.) and Africa (Oryza glaberrima Steud.) discussed as primary centres of domestication. However, until now the pre-Columbian domestication of rice in the Americas has not been documented. Here we document the domestication of Oryza sp. wild rice by the mid-Holocene residents of the Monte Castelo shell mound starting at approximately 4,000 cal. yr BP, evidenced by increasingly larger rice husk phytoliths. Our data provide evidence for the domestication of wild rice in a region of the Amazon that was also probably the cradle of domestication of other major crops such as cassava (Manihot esculenta), peanut (Arachis hypogaea) and chilli pepper (Capsicum sp.). These results underline the role of wetlands as prime habitats for plant domestication worldwide.The research was funded by the European Research Council project âPre-Columbian Amazon-Scale Transformationsâ (ERC-CoG 616179) to J.I. L.M.H. was funded by CAPES (Ministry of Education, Brazil) and Monte Castelo fieldwork was funded by grants from the Brazilian National Science Development Council (CNPq-307179/2013-3) and The National Geographic Society (W243-12) to E.G.N
A Contour Integral Representation for the Dual Five-Point Function and a Symmetry of the Genus Four Surface in R6
The invention of the "dual resonance model" N-point functions BN motivated
the development of current string theory. The simplest of these models, the
four-point function B4, is the classical Euler Beta function. Many standard
methods of complex analysis in a single variable have been applied to elucidate
the properties of the Euler Beta function, leading, for example, to analytic
continuation formulas such as the contour-integral representation obtained by
Pochhammer in 1890. Here we explore the geometry underlying the dual five-point
function B5, the simplest generalization of the Euler Beta function. Analyzing
the B5 integrand leads to a polyhedral structure for the five-crosscap surface,
embedded in RP5, that has 12 pentagonal faces and a symmetry group of order 120
in PGL(6). We find a Pochhammer-like representation for B5 that is a contour
integral along a surface of genus five. The symmetric embedding of the
five-crosscap surface in RP5 is doubly covered by a symmetric embedding of the
surface of genus four in R6 that has a polyhedral structure with 24 pentagonal
faces and a symmetry group of order 240 in O(6). The methods appear
generalizable to all N, and the resulting structures seem to be related to
associahedra in arbitrary dimensions.Comment: 43 pages and 44 figure
The puzzling case of the radio-loud QSO 3C 186: a gravitational wave recoiling black hole in a young radio source?
Context. Radio-loud AGNs with powerful relativistic jets are thought to be
associated with rapidly spinning black holes (BHs). BH spin-up may result from
a number of processes, including accretion of matter onto the BH itself, and
catastrophic events such as BH-BH mergers. Aims. We study the intriguing
properties of the powerful (L_bol ~ 10^47 erg s^-1) radio-loud quasar 3C 186.
This object shows peculiar features both in the images and in the spectra.
Methods. We utilize near-IR Hubble Space Telescope (HST) images to study the
properties of the host galaxy, and HST UV and Sloan Digital Sky Survey optical
spectra to study the kinematics of the source. Chandra X-ray data are also used
to better constrain the physical interpretation. Results. HST imaging shows
that the active nucleus is offset by 1.3 +- 0.1 arcsec (i.e. ~11 kpc) with
respect to the center of the host galaxy. Spectroscopic data show that the
broad emission lines are offset by -2140 +-390 km/s with respect to the narrow
lines. Velocity shifts are often seen in QSO spectra, in particular in
high-ionization broad emission lines. The host galaxy of the quasar displays a
distorted morphology with possible tidal features that are typical of the late
stages of a galaxy merger. Conclusions. A number of scenarios can be envisaged
to account for the observed features. While the presence of a peculiar outflow
cannot be completely ruled out, all of the observed features are consistent
with those expected if the QSO is associated with a gravitational wave (GW)
recoiling BH. Future detailed studies of this object will allow us to confirm
this type of scenario and will enable a better understanding of both the
physics of BH-BH mergers and the phenomena associated with the emission of GW
from astrophysical sources.Comment: 16 pages, 8 figures. Accepted for publication in Astronomy &
Astrophysics. New appendix adde
Toward an understanding of risk factors for anorexia nervosa: A case-control study
Prospective, longitudinal studies of risk factors for anorexia nervosa (AN) are lacking and existing cross-sectional studies are generally narrow in focus and lack methodological rigor. Building on two studies that used the Oxford Risk Factor Interview (RFI) to establish time precedence and comprehensively assess potential risk correlates for AN, the present study advances this line of research and represents the first case-control study of risk factors for AN in the USA
Time-Dependent Vacuum Energy Induced by D-Particle Recoil
We consider cosmology in the framework of a `material reference system' of D
particles, including the effects of quantum recoil induced by closed-string
probe particles. We find a time-dependent contribution to the cosmological
vacuum energy, which relaxes to zero as for large times . If
this energy density is dominant, the Universe expands with a scale factor . We show that this possibility is compatible with recent
observational constraints from high-redshift supernovae, and may also respect
other phenomenological bounds on time variation in the vacuum energy imposed by
early cosmology.Comment: 14 pages LATEX, no figure
H0LiCOW XII. Lens mass model of WFI2033-4723 and blind measurement of its time-delay distance and
We present the lens mass model of the quadruply-imaged gravitationally lensed
quasar WFI2033-4723, and perform a blind cosmographical analysis based on this
system. Our analysis combines (1) time-delay measurements from 14 years of data
obtained by the COSmological MOnitoring of GRAvItational Lenses (COSMOGRAIL)
collaboration, (2) high-resolution imaging,
(3) a measurement of the velocity dispersion of the lens galaxy based on
ESO-MUSE data, and (4) multi-band, wide-field imaging and spectroscopy
characterizing the lens environment. We account for all known sources of
systematics, including the influence of nearby perturbers and complex
line-of-sight structure, as well as the parametrization of the light and mass
profiles of the lensing galaxy. After unblinding, we determine the effective
time-delay distance to be , an average
precision of . This translates to a Hubble constant , assuming a flat CDM
cosmology with a uniform prior on in the range [0.05, 0.5].
This work is part of the Lenses in COSMOGRAIL's Wellspring (H0LiCOW)
collaboration, and the full time-delay cosmography results from a total of six
strongly lensed systems are presented in a companion paper (H0LiCOW XIII).Comment: Version accepted by MNRAS. 29 pages including appendix, 17 figures, 6
tables. arXiv admin note: text overlap with arXiv:1607.0140
A fully relativistic radial fall
Radial fall has historically played a momentous role. It is one of the most
classical problems, the solutions of which represent the level of understanding
of gravitation in a given epoch. A {\it gedankenexperiment} in a modern frame
is given by a small body, like a compact star or a solar mass black hole,
captured by a supermassive black hole. The mass of the small body itself and
the emission of gravitational radiation cause the departure from the geodesic
path due to the back-action, that is the self-force. For radial fall, as any
other non-adiabatic motion, the instantaneous identity of the radiated energy
and the loss of orbital energy cannot be imposed and provide the perturbed
trajectory. In the first part of this letter, we present the effects due to the
self-force computed on the geodesic trajectory in the background field.
Compared to the latter trajectory, in the Regge-Wheeler, harmonic and all
others smoothly related gauges, a far observer concludes that the self-force
pushes inward (not outward) the falling body, with a strength proportional to
the mass of the small body for a given large mass; further, the same observer
notes an higher value of the maximal coordinate velocity, this value being
reached earlier on during infall. In the second part of this letter, we
implement a self-consistent approach for which the trajectory is iteratively
corrected by the self-force, this time computed on osculating geodesics.
Finally, we compare the motion driven by the self-force without and with
self-consistent orbital evolution. Subtle differences are noticeable, even if
self-force effects have hardly the time to accumulate in such a short orbit.Comment: To appear in Int. J. Geom. Meth. Mod. Phy
Gravitation, electromagnetism and the cosmological constant in purely affine gravity
The Eddington Lagrangian in the purely affine formulation of general
relativity generates the Einstein equations with the cosmological constant. The
Ferraris-Kijowski purely affine Lagrangian for the electromagnetic field, which
has the form of the Maxwell Lagrangian with the metric tensor replaced by the
symmetrized Ricci tensor, is dynamically equivalent to the Einstein-Maxwell
Lagrangian in the metric formulation. We show that the sum of the two affine
Lagrangians is dynamically inequivalent to the sum of the analogous Lagrangians
in the metric-affine/metric formulation. We also show that such a construction
is valid only for weak electromagnetic fields. Therefore the purely affine
formulation that combines gravitation, electromagnetism and the cosmological
constant cannot be a simple sum of terms corresponding to separate fields.
Consequently, this formulation of electromagnetism seems to be unphysical,
unlike the purely metric and metric-affine pictures, unless the electromagnetic
field couples to the cosmological constant.Comment: 14 pages, extended and combined with gr-qc/0701176; published versio
Novel colours and the content of experience
I propose a counterexample to naturalistic representational theories of phenomenal character. The counterexample is generated by experiences of novel colours reported by Crane and Piantanida. I consider various replies that a representationalist might make, including whether novel colours could be possible colours of objects and whether one can account for novel colours as one would account for binary colours or colour mixtures. I argue that none of these strategies is successful and therefore that one cannot fully explain the nature of the phenomenal character of perceptual experiences using a naturalistic conception of representation
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