2,057 research outputs found
The existence and detection of optically dark galaxies by 21cm surveys
One explanation for the disparity between Cold Dark Matter (CDM) predictions
of galaxy numbers and observations could be that there are numerous dark
galaxies in the Universe. These galaxies may still contain baryons, but no
stars, and may be detectable in the 21cm line of atomic hydrogen. The results
of surveys for such objects, and simulations that do/do not predict their
existence, are controversial. In this paper we use an analytical model of
galaxy formation, consistent with CDM, to firstly show that dark galaxies are
certainly a prediction of the model. Secondly, we show that objects like
VIRGOHI21, a dark galaxy candidate recently discovered by us, while rare are
predicted by the model. Thirdly, we show that previous 'blind' HI surveys have
placed few constraints on the existence of dark galaxies. This is because they
have either lacked the sensitivity and/or velocity resolution or have not had
the required detailed optical follow up. We look forward to new 21cm blind
surveys (ALFALFA and AGES) using the Arecibo multi-beam instrument which should
find large numbers of dark galaxies if they exist
The effects of diet and mating system on reproductive (and postâreproductive) life span in a freshwater snail
The length of the reproductive life span, along with the number/frequency/magnitude of reproductive events, quantifies an individualâs potential contribution to the next generation. By examining reproductive life span, and distinguishing it from somatic life span, we gain insight into critical aspects of an individualâs potential fitness as well as reproductive and somatic senescence. Additionally, differentiating somatic and reproductive life spans can provide insight into the existence of a postâreproductive period and factors that shape its duration. Given the known importance of diet and mating system on resource allocation, I reared individual freshwater snails (Physa acuta) from 22 fullâsib families under a 2 Ă 2 factorial design that crossed mate availability (available [outcrossing] or not [selfing]) and diet (Spirulina or lettuce) and quantified aspects of the entire life history enabling me to distinguish reproductive and somatic life spans, determine the total number of reproductive events, and evaluate how the reproductive rate changes with age. Overall, mated snails experienced shorter reproductive and somatic life spans; a diet of Spirulina also shortened both reproductive and somatic life spans. A postâreproductive period existed in all conditions; its duration was proportional to somatic but not reproductive life span. I evaluate several hypotheses for the existence and duration of the postâreproductive period, including a novel hypothesis that the postâreproductive period may result from an increase in reproductive interval with age. I conclude that the postâreproductive period may be indicative of a randomly timed death occurring as the interval between reproductive events continues to increase. As such, a âpostâreproductiveâ period can be viewed as a byâproduct of a situation where reproductive senescence outpaces somatic senescence
SKA HI end2end simulation
The current status of the HI simulation efforts is presented, in which a self
consistent simulation path is described and basic equations to calculate array
sensitivities are given. There is a summary of the SKA Design Study (SKADS) sky
simulation and a method for implementing it into the array simulator is
presented. A short overview of HI sensitivity requirements is discussed and
expected results for a simulated HI survey are presented.Comment: 7 pages, 6 figues, need skads2009.cls file to late
Annotated Checklist of the Avian Species Observed at the Gordon Natural Area (West Chester University, PA) 2004-2020. Version IX. Data from eBird (through 7/20/2020) and from the 2004 West Chester Bird Club Survey of the GNA.ersion IX.
Summary Data Number of Surveys: 108 \u27Site Visits\u27 by 28 Birders. Note: this does not count the birders who participated in the 2004 West Chester Bird Club Survey as they were not identified on the species checklist. Number of Taxa: 125 Species, in 86 Genera and 38 Families. Abundances The color of each month\u27s \u27box\u27 represents the average number of individuals observed during all surveys during that month (see key at the bottom of the page). The first number within the \u27box\u27 for each month represents the number of days in which that species was observed during the month; the second number represents the total number of days of surveying for that month. Audubon Priority Birds: are birds of significant conservation need, for which our actions, over time, can lead to measurable improvements in status (Audubon 2020a). PBS Status Data are from the Pennsylvania Biological Survey (PBS 2020). IUCN Status: Data are from the The IUCN Red List of Threatened Species (IUCN 2020). Threats The 2014 climate threat assessment data are from Audubon (2020b). The 2020 climate threat assessment data (Audubon 2020c) were compiled from a query based on species\u27 statuses in Zip Code 19383 and a query for species\u27 statuses in Pennsylvania. The default was data for Zip Code 19383, whenever these were available. Foraging Strategies and Food Sources Data were compiled from the Audubon Guide to North American Birds website (Audubon 2020d). Ground Foraging Species (i.e., species that are either ground foragers or foliage-gleaners and which forage on invertebrates) were determined based on Conover (2011)
Checklist of the avian species observed at the Gordon Natural Area (West Chester University, PA) 2004-2018. Version VII. Latest observations from eBird: 3/23/2018
Avian Species Observed at the Gordon Natural Area (Data from eBird and the 2004 West Chester Bird Club Survey of the GNA)
The Arecibo Galaxy Environments survey IV: the NGC7448 region and the HI mass function
In this paper we describe results from the Arecibo Galaxy Environments Survey
(AGES). The survey reaches column densities of ~3x10^18 cm^-2 and masses of
~10^7 M_O, over individual regions of order 10 sq deg in size, out to a maximum
velocity of 18,000 km s^-1. Each surveyed region is centred on a nearby galaxy,
group or cluster, in this instance the NGC7448 group. Galaxy interactions in
the NGC7448 group reveal themselves through the identification of tidal tails
and bridges. We find ~2.5 times more atomic gas in the inter-galactic medium
than in the group galaxies. We identify five new dwarf galaxies, two of which
appear to be members of the NGC7448 group. This is too few, by roughly an order
of magnitude, dwarf galaxies to reconcile observation with theoretical
predictions of galaxy formation models. If they had observed this region of sky
previous wide area blind HI surveys, HIPASS and ALFALFA, would have detected
only 5% and 43% respectively of the galaxies we detect, missing a large
fraction of the atomic gas in this volume. We combine the data from this paper
with that from our other AGES papers (370 galaxies) to derive a HI mass
function with the following Schechter function parameters alpha=-1.52+/-0.05,
M^*=5.1+/-0.3x10^9 h_72^-2 M_O, phi=8.6+/-1.1x10-3 h_72^3 Mpc^-3 dex-1.
Integrating the mass function leads to a cosmic mass density of atomic hydrogen
of Omega_HI=5.3+/-0.8x10^-4 h_72^-1. Our mass function is steeper than that
found by both HIPASS and ALFALFA (alpha=1.37 and 1.33 respectively), while our
cosmic mass density is consistent with ALFALFA, but 1.7 times larger than found
by HIPASS
Superconducting Qubits Coupled to Nanoelectromechanical Resonators: An Architecture for Solid-State Quantum Information Processing
We describe the design for a scalable, solid-state
quantum-information-processing architecture based on the integration of
GHz-frequency nanomechanical resonators with Josephson tunnel junctions, which
has the potential for demonstrating a variety of single- and multi-qubit
operations critical to quantum computation. The computational qubits are
eigenstates of large-area, current-biased Josephson junctions, manipulated and
measured using strobed external circuitry. Two or more of these phase qubits
are capacitively coupled to a high-quality-factor piezoelectric
nanoelectromechanical disk resonator, which forms the backbone of our
architecture, and which enables coherent coupling of the qubits. The integrated
system is analogous to one or more few-level atoms (the Josephson junction
qubits) in an electromagnetic cavity (the nanomechanical resonator). However,
unlike existing approaches using atoms in electromagnetic cavities, here we can
individually tune the level spacing of the ``atoms'' and control their
``electromagnetic'' interaction strength. We show theoretically that quantum
states prepared in a Josephson junction can be passed to the nanomechanical
resonator and stored there, and then can be passed back to the original
junction or transferred to another with high fidelity. The resonator can also
be used to produce maximally entangled Bell states between a pair of Josephson
junctions. Many such junction-resonator complexes can assembled in a
hub-and-spoke layout, resulting in a large-scale quantum circuit. Our proposed
architecture combines desirable features of both solid-state and cavity quantum
electrodynamics approaches, and could make quantum information processing
possible in a scalable, solid-state environment.Comment: 20 pages, 14 separate low-resolution jpeg figure
Diet alters delayed selfing, inbreeding depression, and reproductive senescence in a freshwater snail
Reproductive success is a critical fitness attribute that is directly influenced by resource availability. Here, we investigate the effects of diet-based resource availability on three interrelated aspects of reproductive success: a change in mating system based on mate availability, consequent inbreeding depression, and the deterioration of reproductive efficiency with age (senescence). We employed a factorial experimental design using 22 full-sib families of the hermaphroditic freshwater snail Physa acuta to explore these interactions. Individual snails were reared in one of two mate-availability treatments (isolated [selfing] or occasionally paired [outcrossing]) and one of two diet treatments (boiled lettuce or Spirulina, an algae that is rich in protein, vitamins, and minerals). Spirulina-fed snails initiated reproduction at a 13% earlier age and 7% larger size than lettuce-fed snails. Spirulina also resulted in a 30% reduction in the time delay before selfing. Compared to lettuce, a diet of Spirulina increased inbreeding depression by 52% for egg hatching rate and 64% for posthatching juvenile survival. Furthermore, Spirulina led to a 15-fold increase in the rate of reproductive senescence compared with a diet of lettuce. These transgenerational, interactive effects of diet on inbreeding depression and reproductive senescence are discussed in the context of diet-induced phenotypic plasticity
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