The focus of dark matter searches to date has been on Weakly Interacting Massive Particles (WIMPs) in the GeV/
c
2
-TeV/
c
2
mass range. The direct, indirect and collider searches in this mass range ...have been extensive but ultimately unsuccessful, providing a strong motivation for widening the search outside this range. Here we describe a new concept for a dark matter experiment, employing superfluid
3
He as a detector for dark matter that is close to the mass of the proton, of order 1 GeV/
c
2
. The QUEST-DMC detector concept is based on quasiparticle detection in a bolometer cell by a nanomechanical resonator. In this paper we develop the energy measurement methodology and detector response model, simulate candidate dark matter signals and expected background interactions, and calculate the sensitivity of such a detector. We project that such a detector can reach sub-eV nuclear recoil energy threshold, opening up new windows on the parameter space of both spin-dependent and spin-independent interactions of light dark matter candidates.
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Direct measurements of reversible magnetic-field-induced strain (MFIS) on a single crystalline Ni45Co5Mn36.5In13.5 metamagnetic shape memory alloy were attained via magnetic-field-induced martensitic ...transformation under different stress levels and at various temperatures. This was achieved using a custom-designed micro-magneto-thermo-mechanical testing system capable of applying constant stress while measuring strain and magnetization simultaneously on the samples, which can fit into conventional superconducting magnets. MFIS levels are reported as a function of temperature, magnetic field and external bias stress. It was necessary to apply an external bias stress in these materials to detect a notable MFIS because a magnetic field does not favor a specific martensite variant resulting in no shape change even though magnetic field leads to reversible martensitic transformation. Fully recoverable transformation strains up to 3.10% were detected under repeated field applications in the presence of different compressive stress levels up to 125MPa. The bias stress opposes the field-induced martensite-to-austenite phase transformation and causes the critical field for the transformation to increase at a given temperature in accordance with the Clausius Clapeyron relationship. The effect of the bias stress on the kinetic arrest of austenite is also explored.
Sub-Saharan Africa has long been seen as lacking the potential for autochthonous urban development, and Near Eastern and European contact provided ready explanations for the emergence of precolonial ...cities across the continent. In the past few decades, the pace of archaeological work on African cities has accelerated, and archaeologists have increasingly deployed a functional model of the city, in which cities are defined in relation to broader hinterlands rather than particular traits. As a result, deeply rooted urban traditions have been identified in all corners of the continent. Despite the antiquity of urban traditions across Africa, however, long-distance forces clearly had wide-reaching impacts on urban developmental trajectories, and proponents of the functional model have yet to explain the specific role of long-distance forces in the process of urbanization. This review examines how multiscalar forces shaped urban trajectories in West Africa, specifically. I examine how local political entrepreneurs took advantage of the opportunities provided by local, interregional, and global forces, resulting in a heterogeneous set of urban traditions across West Africa, ranging from trading entrepôts to regional capitals. Throughout I emphasize how local agency articulated with multiscalar social and economic forces, transforming the nature of regional integration, economic specialization, and the materialization of social difference, defining qualities of urban life.
New neutrino–nucleus interaction cross-section measurements are required to improve nuclear models sufficiently for future long baseline neutrino experiments to meet their sensitivity goals. A time ...projection chamber (TPC) filled with a high-pressure gas is a promising detector to characterise the neutrino sources used for such experiments. A gas-filled TPC is ideal for measuring low-energy particles, which travel further in gas than in solid or liquid detectors and using high-pressure increases the target density, resulting in more neutrino interactions. We examine the suitability of multiwire proportional chambers (MWPCs) from the ALICE TPC for use as the readout chambers of a high-pressure gas TPC. These chambers were previously operated at atmospheric pressure. We report the successful operation of an ALICE TPC outer readout chamber (OROC) at pressures up to 4.2 bar absolute (barA) with
Ar-CH
4
mixtures with a
CH
4
content between 2.8 and 5.0%, and so far up to 4 bar absolute with
Ar-CO
2
(90-10). The charge gain of the OROC was measured with signals induced by an
55
Fe
source. The largest gain achieved at 4.2 bar was
(
29
±
1
)
·
10
3
in
Ar-CH
4
with 4.0%
CH
4
with an anode voltage of
2975
V
. In
Ar-CO
2
with 10%
CO
2
at 4 barA, a gain of
(
4.2
±
0.1
)
·
10
3
was observed with anode voltage
2975
V
. We extrapolate that at 10 barA, an interesting pressure for future neutrino experiments, a gain of 5000 in
Ar-CO
2
with 10%
CO
2
(10,000 in
Ar-CH
4
with
∼
4
%
CH
4
) may be achieved with anode voltage of
4.6
kV
(
∼
3.6
kV
).
Celotno besedilo
Dostopno za:
DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, SIK, UILJ, UKNU, UL, UM, UPUK
Sympatric sister species generally have a degree of phenotypic differentiation that allows them to coexist. It has been well documented that phenotypic similarity results, through resource ...competition, in one of two major outcomes: local extinction of either competitor or character displacement. Limiting similarity suggests that there is a maximum degree of phenotypic niche overlap with which similar species may coexist. Breaching that maximum would result in exclusion. Character displacement, on the other hand, implies that the species differentiate phenotypically so that resource competition is reduced to the point where coexistence is possible. While it has been suggested that these theories have the potential to accelerate (character displacement) or limit phenotypic evolution (competitive exclusion) on microevolutionary time scales, their effects on macroevolution remain under‐studied. If competition accelerates evolution on a macroevolutionary scale, one would expect that phenotypic diversity increases as novel species ‘push aside’ existing species. On the other hand, one might also expect that phenotypic evolution comes to a halt as novel species are trapped in the (ever decreasing) phenotypic space not yet occupied by existing species, except at the extremes of the phenotypic spectrum. Studying the current geographical ranges of more than 3000 extant species representing 29 mammalian families and their respective body masses, I found little evidence of competition accelerating body size differentiation between species.
Sexual size dimorphism (SSD) is one of the most common ways in which males and females differ. Male‐biased SSD (when males are larger) is often attributed to sexual selection favouring large males. ...When females are larger (female‐biased SSD), it is often argued that natural selection favouring increased fecundity (i.e. larger clutches or eggs) has coevolved with larger female body size. Using comparative phylogenetic and multispecies regression model selection approaches, we test the hypothesis that among‐species variation in female fecundity is associated with the evolution of female‐biased SSD. We also ask whether the hypothesized relationship between SSD and fecundity is relaxed upon the evolution of parental care. Our results suggest a strong relationship between the evolution of fecundity and body size, but we find no significant relationship between fecundity and SSD. Similarly, there does not appear to be a relationship between fecundity and the presence or absence of parental care among species. Thus, although female body size and fecundity coevolve, selection for increased fecundity as an explanation for female‐biased SSD is inconsistent with our analyses. We caution that a relationship between female body size and fecundity is insufficient evidence for fecundity selection driving the evolution of female‐biased SSD.
Sensory hair cells are the mechanotransductive receptors that detect gravity, sound, and vibration in all vertebrates. Damage to these sensitive receptors often results in deficits in vestibular ...function and hearing. There are currently two main reasons for studying the process of hair cell loss in fishes. First, fishes, like other non-mammalian vertebrates, have the ability to regenerate hair cells that have been damaged or lost via exposure to ototoxic chemicals or acoustic overstimulation. Thus, they are used as a biomedical model to understand the process of hair cell death and regeneration and find therapeutics that treat or prevent human hearing loss. Secondly, scientists and governmental natural resource managers are concerned about the potential effects of intense anthropogenic sounds on aquatic organisms, including fishes. Dr. Arthur N. Popper and his students, postdocs and research associates have performed pioneering experiments in both of these lines of fish hearing research. This review will discuss the current knowledge regarding the causes and consequences of both lateral line and inner ear hair cell damage in teleost fishes.
Genetic parentage analyses reveal considerable diversity in alternative reproductive behaviours (e.g. sneaking) in many taxa. However, little is known about whether these behaviours vary seasonally ...and between populations. Here, we investigate seasonal variation in male reproductive behaviours in a population of two‐spotted gobies (Gobiusculus flavescens) in Norway. Male two‐spotted gobies guard nests, attract females and care for fertilized eggs. We collected clutches and nest‐guarding males early and late in the breeding season in artificial nests and used microsatellite markers to reconstruct parentage from a subset of offspring from each nest. We hypothesized that mating, reproductive success and sneaking should be more prevalent early in the breeding season when competition for mates among males is predicted to be higher. However, parentage analyses revealed similar values of mating, reproductive success and high frequencies of successful sneaking early (30% of nests) and late (27% of nests) in the season. We also found that multiple females with eggs in the same nest were fertilized by one or more sneaker males, indicating that some males in this population engage in a satellite strategy. We contrast our results to previous work that demonstrates low levels of cuckoldry in a population in Sweden. Our results demonstrate marked stability in both the genetic mating system and male alternative reproductive tactics over the breeding season. However, sneaking rates may vary geographically within a species, likely due to local selection influencing ecological factors encountered at different locations.
•Thermocouples installed in oscillating heat pipe (OHP) for fluid temperature measurements.•Conduction along tube wall of OHP can be ∼10% of the overall heat transfer.•Tubular OHP measured to have ...internal Nusselt number between 4 and 6.•Internal OHP temperature oscillations have larger amplitudes than external.•Thermal conductivity of OHP is higher when considering internal fluid temperatures.
The current study examines the relationship between internal/fluidic and external/wall temperature measurements along the adiabatic section of an operating tubular oscillating heat pipe (T-OHP) for varying heat inputs. Temperature measurements were achieved using type-T thermocouples located either inside or along the OHP wall in the region between the evaporator and condenser. Measurements were utilized to elucidate the effects of wall thermal capacitance, external wall temperature gradient, and internal fluid advection. The internal, single-phase heat transfer coefficient was estimated, and the effective thermal conductivity of the OHP was determined. A 4-turn copper T-OHP (3.25mm ID) was charged with water (75% by volume) and tested in the bottom-heating condition. Heat input was varied in increments of 25W from 60W to 300W. Results indicate that the external thermocouples were unable to capture frequency components larger than ∼1Hz. Internal measurements indicate that average, evaporator-side fluid oscillation frequencies varied from ∼1.5Hz at 60W to ∼2.5Hz at 300W, whereas condenser-side frequencies remained fairly constant at ∼0.5Hz. The frequency transfer function corresponding to the thermal resistance network between the internal/external thermocouples was found to be constant across all tested power inputs. The low-frequency, large-amplitude changes in internal temperature associated with bulk fluid motion were not immediately measured at the external OHP tube surface. The effective thermal conductivity calculated using only external temperature measurements was found to be 4–12% lower than that calculated using internal measurements. The maximum, calculated effective thermal conductivity using internal or external temperature measurements was 15,300W/m·K and 14,000W/m·K, respectively. This difference arises from there being a smaller, length-wise temperature gradient along the fluid columns than along the tube wall due to the strong advection component of OHP heat transfer. Tube wall conduction was found to account for 2–10% of the overall heat transfer, with its significance decreasing as fluid advection increased at higher heat inputs. The heat transfer coefficient for single-phase fluid oscillation inside the OHP was estimated to be ∼1000W/m2K for power inputs larger than 100W; corresponding to Nusselt numbers between 4 and 6.
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