5,783 research outputs found
Taxonomic decomposition of the latitudinal gradient in species diversity of North American floras
Aim: To test the latitudinal gradient in plant species diversity for self-similarity across taxonomic scales and amongst taxa. Location: North America. Methods: We used species richness data from 245 local vascular plant floras to quantify the slope and shape of the latitudinal gradients in species diversity (LGSD) across all plant species as well as within each family and order. We calculated the contribution of each family and order to the empirical LGSD. Results: We observed the canonical LGSD when all plants were considered with floras at the lowest latitudes having, on average, 451 more species than floras at the highest latitudes. When considering slope alone, most orders and families showed the expected negative slope, but 31.7% of families and 27.7% of orders showed either no significant relationship between latitude and diversity or a reverse LGSD. Latitudinal patterns of family diversity account for at least 14% of this LGSD. Most orders and families did not show the negative slope and concave-down quadratic shape expected by the pattern for all plant species. A majority of families did not make a significant contribution in species to the LGSD with 53% of plant families contributing little to nothing to the overall gradient. Ten families accounted for more than 70% of the gradient. Two families, the Asteraceae and Fabaceae, contributed a third of the LGSD. Main Conclusions: The empirical LGSD we describe here is a consequence of a gradient in the number of families and diversification within relative few plant families. Macroecological studies typically aim to generate models that are general across taxa with the implicit assumption that the models are general within taxa. Our results strongly suggest that models of the latitudinal gradient in plant species richness that rely on environmental covariates (e.g. temperature, energy) are likely not general across plant taxa
Spectral weight transfer in a disorder-broadened Landau level
In the absence of disorder, the degeneracy of a Landau level (LL) is
, where is the magnetic field, is the area of the sample
and is the magnetic flux quantum. With disorder, localized states
appear at the top and bottom of the broadened LL, while states in the center of
the LL (the critical region) remain delocalized. This well-known phenomenology
is sufficient to explain most aspects of the Integer Quantum Hall Effect (IQHE)
[1]. One unnoticed issue is where the new states appear as the magnetic field
is increased. Here we demonstrate that they appear predominantly inside the
critical region. This leads to a certain ``spectral ordering'' of the localized
states that explains the stripes observed in measurements of the local inverse
compressibility [2-3], of two-terminal conductance [4], and of Hall and
longitudinal resistances [5] without invoking interactions as done in previous
work [6-8].Comment: 5 pages 3 figure
Oldest directly dated remains of sheep in China
The origins of domesticated sheep (Ovis sp.) in China remain unknown. Previous workers have speculated that sheep may have been present in China up to 7000 years ago, however many claims are based on associations with archaeological material rather than independent dates on sheep material. Here we present 7 radiocarbon dates on sheep bone from Inner Mongolia, Ningxia and Shaanxi provinces. DNA analysis on one of the bones confirms it is Ovis sp. The oldest ages are about 4700 to 4400 BCE and are thus the oldest objectively dated Ovis material in eastern Asia. The graphitisised bone collagen had δ13C values indicating some millet was represented in the diet. This probably indicates sheep were in a domestic setting where millet was grown. The younger samples had δ13C values indicating that even more millet was in the diet, and this was likely related to changes in foddering practices. Š 2014, Macmillan Publishers Limite
Calculating Unknown Eigenvalues with a Quantum Algorithm
Quantum algorithms are able to solve particular problems exponentially faster
than conventional algorithms, when implemented on a quantum computer. However,
all demonstrations to date have required already knowing the answer to
construct the algorithm. We have implemented the complete quantum phase
estimation algorithm for a single qubit unitary in which the answer is
calculated by the algorithm. We use a new approach to implementing the
controlled-unitary operations that lie at the heart of the majority of quantum
algorithms that is more efficient and does not require the eigenvalues of the
unitary to be known. These results point the way to efficient quantum
simulations and quantum metrology applications in the near term, and to
factoring large numbers in the longer term. This approach is architecture
independent and thus can be used in other physical implementations
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Toward a theory for diversity gradients: the abundanceâadaptation hypothesis
The abundanceâadaptation hypothesis argues that taxa with more individuals and faster generation times will have more evolutionary âexperimentsâ allowing expansion into, and diversification within, novel habitats. Thus, as older taxa have produced more individuals over time, and smaller taxa have higher population sizes and faster generation times, the Latitudinal Diversity Gradients (LDGs) of these clades should show shallower slopes. We describe the LDGs for archaea, bacteria, fungi, invertebrates and trees from six North American forests. For three focal groups â bacteria, ants, and trees â older taxa had shallower LDG slopes than the more recent, terminal taxa. Across 12 orders of magnitude of body mass, LDG slopes were steeper in larger taxa. The slopes of LDGs vary systematically with body size and clade age, underscoring the non-canonical nature of LDGs. The steepest LDG slopes were found for the largest organisms while the smallest, from bacteria to small litter-soil invertebrates, have shallower- to zero-slope LDGs. If tropical niche conservatism is the failure of clades to adapt to, and diversify in temperate habitats, then the steep LDGs of chordates and plants likely arise from the decreased ability of clades with large individuals to adapt to the multiple challenges of extra-tropical life
Experimental realisation of Shor's quantum factoring algorithm using qubit recycling
Quantum computational algorithms exploit quantum mechanics to solve problems
exponentially faster than the best classical algorithms. Shor's quantum
algorithm for fast number factoring is a key example and the prime motivator in
the international effort to realise a quantum computer. However, due to the
substantial resource requirement, to date, there have been only four
small-scale demonstrations. Here we address this resource demand and
demonstrate a scalable version of Shor's algorithm in which the n qubit control
register is replaced by a single qubit that is recycled n times: the total
number of qubits is one third of that required in the standard protocol.
Encoding the work register in higher-dimensional states, we implement a
two-photon compiled algorithm to factor N=21. The algorithmic output is
distinguishable from noise, in contrast to previous demonstrations. These
results point to larger-scale implementations of Shor's algorithm by harnessing
scalable resource reductions applicable to all physical architectures.Comment: 7 pages, 3 figure
Online and offline video game use in adolescents: measurement invariance and problem severity
Background:
Despite the increasing popularity of videogame playing, little is known about the similarities and differences between online and offline videogame players. However, the characteristics of online and offline gaming might predispose different pattern of problematic use.
Objectives:
The aims of this study were to (i) test applicability and the measurement invariance of the previously developed Problematic Online Gaming Questionnaire (POGQ) in both online and offline gamers; and (ii) examine the differences between online and offline gamers in the dimensions of problematic use.
Methods:
A total of 1,964 adolescent videogame players were recruited. Information on videogame use habits were collected and all gamers were administered the POGQ. Those gamers who played at least sometimes in an online context were considered as âonline gamersâ and âoffline gamersâ were those who played videogames exclusively offline.
Results:
Confirmatory factor analysis supported the measurement invariance across online and offline videogame players. According to the multiple indicators multiple causes (MIMIC) model, online gamers were more likely to score higher on overuse, interpersonal conflict, and social isolation subscales of the POGQ.
Conclusion:
The results of the present study suggest that online and
offline gaming can be assessed using the same psychometric instrument. These findings open the possibility for future research studies concerning problematic video game to include participants who exclusively play either online or offline games, or both. However, the study also identified important structural features about how online and offline gaming might contribute differently to problematic use. These results provide important information and ideas that could be utilized in parental education and prevention program about the possible detrimental consequences of online vs. offline video game use
Regulation of aldosterone secretion by Ca(v)1.3
This work is supported by NIHR Senior Investigator grant NF-SI-0512-10052 awarded to M.J.B.; the Austin Doyle Award (Servier Australia) and the Tunku Abdul Rahman Centenary Fund (St Catharine's College, Cambridge, UK) awarded to E.A.B.A.; Gates Cambridge Scholarship awarded to C.B.X.; L.H.S., S.G. and C.M. are supported by the British Heart Foundation PhD studentship FS/11/35/28871, FS/14/75/31134 and FS/14/12/30540 respectively; J.Z. was supported by the Cambridge Overseas Trust Scholarship and the Sun Hung Kai Properties-Kwoksâ Foundation; A.E.D.T. is funded by the Agency for Science, Technology & Research (A*STAR) Singapore and Wellcome Trust Award 085686/Z/08/A; LHS, JZ and EABA were further supported by the NIHR Cambridge Biomedical Research Centre; the Human Research Tissue Bank is supported by the NIHR Cambridge Biomedical Research Centre. The Cav1.3 constructs were kindly gifted by Dr. Joerg Striessnig and Dr Petronel Tuluc
Diminished temperature and vegetation seasonality over northern high latitudes
Global temperature is increasing, especially over northern lands (>50°âN), owing to positive feedbacks1. As this increase is most pronounced in winter, temperature seasonality (ST)âconventionally defined as the difference between summer and winter temperaturesâis diminishing over time2, a phenomenon that is analogous to its equatorward decline at an annual scale. The initiation, termination and performance of vegetation photosynthetic activity are tied to threshold temperatures3. Trends in the timing of these thresholds and cumulative temperatures above them may alter vegetation productivity, or modify vegetation seasonality (SV), over time. The relationship between ST and SV is critically examined here with newly improved ground and satellite data sets. The observed diminishment of ST and SV is equivalent to 4° and 7° (5° and 6°) latitudinal shift equatorward during the past 30 years in the Arctic (boreal) region. Analysis of simulations from 17 state-of-the-art climate models4 indicates an additional STdiminishment equivalent to a 20° equatorward shift could occur this century. How SV will change in response to such large projected ST declines and the impact this will have on ecosystem services5 are not well understood. Hence the need for continued monitoring6 of northern lands as their seasonal temperature profiles evolve to resemble thosefurther south.Lopullinen vertaisarvioitu käsikirjoitu
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