259 research outputs found
Recommended from our members
Investigating xylem embolism formation, refilling and water storage in tree trunks using frequency domain reflectometry
Trunks of large trees play an important role in whole-plant water balance but technical difficulties have limited most hydraulic research to small stems, leaves, and roots. To investigate the dynamics of water-related processes in tree trunks, such as winter embolism refilling, xylem hydraulic vulnerability, and water storage, volumetric water content (VWC) in the main stem was monitored continuously using frequency domain moisture sensors in adult Betula papyrifera trees from early spring through the beginning of winter. An air injection technique was developed to estimate hydraulic vulnerability of the trunk xylem. Trunk VWC increased in early spring and again in autumn, concurrently with root pressure during both seasons. Diurnal fluctuations and a gradual decrease in trunk VWC through the growing season were observed, which, in combination with VWC increase after significant rainfall events and depletion during periods of high water demand, indicate the importance of stem water storage in both short- and long-term water balance. Comparisons between the trunk air injection results and conventional branch hydraulic vulnerability curves showed no evidence of ‘vulnerability segmentation’ between the main stem and small branches in B. papyrifera. Measurements of VWC following air injection, together with evidence from air injection and xylem dye perfusion, indicate that embolized vessels can be refilled by active root pressure but not in the absence of root pressure. The precise, continuous, and non-destructive measurement of wood water content using frequency domain sensors provides an ideal way to probe many hydraulic processes in large tree trunks that are otherwise difficult to investigate.Organismic and Evolutionary Biolog
Investigating the topological structure of quenched lattice QCD with overlap fermions by using multi-probing approximation
The topological charge density and topological susceptibility are determined
by multi-probing approximation using overlap fermions in quenched SU(3) gauge
theory. Then we investigate the topological structure of the quenched QCD
vacuum, and compare it with results from the all-scale topological density, the
results are consistent. Random permuted topological charge density is used to
check whether these structures represent underlying ordered properties.
Pseudoscalar glueball mass is extracted from the two-point correlation function
of the topological charge density. We study ensembles of different lattice
spacing with the same lattice volume , the results are
compatible with the results of all-scale topological charge density, and the
topological structures revealed by multi-probing are much closer to all-scale
topological charge density than that by eigenmode expansion.Comment: 12 pages,34 figure
Strangelets at finite temperature: nucleon emission rates, interface and shell effects
We investigate the properties of strangelets at finite temperature , where
an equivparticle model is adopted with both the linear confinement and
leading-order perturbative interactions accounted for using density-dependent
quark masses. The shell effects are examined by solving the Dirac equations for
quarks in the mean-field approximation, which diminish with temperature as the
occupation probability of each single-particle levels fixed by the Fermi-Dirac
statistics, i.e., shell dampening. Consequently, instead of decreasing with
temperature, the surface tension extracted from a liquid-drop formula increases
with until reaching its peak at -40 MeV with vanishing shell
corrections, where the formula roughly reproduces the free energy per baryon of
all strangelets. The curvature term, nevertheless, decreases with despite
the presence of shell effects. The neutron and proton emission rates are fixed
microscopically according to the external nucleon gas densities that are in
equilibrium with strangelets, which generally increase with (
MeV) for stable strangelets but decrease for those that are unstable against
nucleon emission at . The energy, free energy, entropy, charge-to-mass
ratio, strangeness per baryon, and root-mean-square radius of -stable
strangelets obtained with various parameter sets are presented as well. The
results indicated in this work are useful for understanding the products of
binary compact star mergers and heavy-ion collisions
Storage of 1650 modes of single photons at telecom wavelength
To advance the full potential of quantum networks one should be able to
distribute quantum resources over long distances at appreciable rates. As a
consequence, all components in the networks need to have large multimode
capacity to manipulate photonic quantum states. Towards this end, a multimode
photonic quantum memory, especially one operating at telecom wavelength,
remains a key challenge. Here we demonstrate a spectro-temporally multiplexed
quantum memory at 1532 nm. Multimode quantum storage of telecom-band heralded
single photons is realized by employing the atomic frequency comb protocol in a
10-m-long cryogenically cooled erbium doped silica fibre. The multiplexing
encompasses five spectral channels - each 10 GHz wide - and in each of these up
to 330 temporal modes, resulting in the simultaneous storage of 1650 modes of
single photons. Our demonstrations open doors for high-rate quantum networks,
which are essential for future quantum internet
Relações hÃdricas e arquitetura hidráulica em árvores do cerrado : adequação à s variações sazonais de disponibilidade hÃdrica e de demanda evaporativa
O objetivo deste estudo foi determinar os ajustamentos na morfologia e fisiologia que
permitem árvores das savanas neotropicais do Brasil Central (Cerrado) de evitar déficits hÃdricos e de manter um balanço
hÃdrico interno praticamente constante apesar das variações sazonais da precipitação e no déficit de saturação do ar (D).
A precipitação na área de estudo é fortemente sazonal, com cerca de cinco meses praticamente sem chuva durante os
quais D é duas vezes maior aos valores medidos na época chuvosa. Como conseqüência da flutuação sazonal das
chuvas e de D, o potencial hÃdrico do solo muda substancialmente, nos primeiros 100 cm do solo, mas permanece quase constante abaixo de 2 m de profundidade. A arquitetura hidráulica e os parâmetros relacionados a relações hÃdricas das
árvores do Cerrado se ajustaram durante a estação seca para evitar o déficit hÃdrico crescente e assegurar a homeostase
nos valores mÃnimos de potencial hÃdrico foliar ΨL e na perda total diária de água pela planta (iso-hidria). O
comportamento iso-hÃdrico das árvores do Cerrado foi o resultado de uma diminuição da superfÃcie foliar total por
árvore, um forte controle estomático das perdas por evaporação, um aumento na condutividade hidráulica especÃfica da
folha e na condutância hidráulica foliar e um aumento da quantidade de águas retirada dos reservatórios internos do
caule, durante a estação seca. A eficiência no transporte de água aumentou, nas mesmas proporções, nas folhas e nos
ramos terminais durante a estação seca. Todos estes ajustamentos sazonais foram importantes para a manutenção de ΨL
acima de limiares crÃticos, com isto contribuindo para uma redução na formação de embolismos nos ramos e ajudando a
evitar a perda de turgor em tecidos foliares durante a época seca. Esses ajustes permitem que os ramos das espécies
lenhosas do Cerrado operem bem distanciados do ponto de disfunção catastrófica para a cavitação, enquanto as folhas
operam próximas e sofrem embolismos em uma base diária, especialmente durante a estação seca.We determined adjustments in physiology and morphology that allow Neotropical savanna trees from central Brazil (Cerrado)
to avoid water deficits and to maintain a nearly constant internal water balance despite seasonal changes in precipitation and
air saturation deficit (D). Precipitation in the study area is highly seasonal with about five nearly rainless months during which
D is two fold higher compared to wet season values. As a consequence of the seasonal fluctuations in rainfall and D, soil water
potential changes substantially in the upper 100 cm of soil, but remains nearly constant below 2 m depth. Hydraulic
architecture and water relations traits of Cerrado trees adjusted during the dry season to prevent increasing water deficits and
insure homeostasis in minimum leaf water potential ΨL and in total daily water loss per plant (isohydry). The isohydric
behavior of Cerrado trees was the result of a decrease in total leaf surface area per tree, a strong stomatal control of
evaporative losses, an increase in leaf-specific hydraulic conductivity and leaf hydraulic conductance and an increase in the
amount of water withdrawn from internal stem storage, during the dry season. Water transport efficiency increased in the same
proportion in leaves and terminal stems during the dry season. All of these seasonal adjustments were important for
maintaining ΨL above critical thresholds, which reduces the rate of embolism formation in stems and help to avoid turgor loss
in leaf tissues still during the dry season. These adjustments allow the stems of most Cerrado woody species to operate far
from the point of catastrophic dysfunction for cavitation, while leaves operate close to it and experience embolism on a daily
basis, especially during the dry season
Effect of dispersion on indistinguishability between single-photon wave-packets
With propagating through a dispersive medium, the temporal-spectral profile
of laser pulses should be inevitably modified. Although such dispersion effect
has been well studied in classical optics, its effect on a single-photon
wave-packet, i.e., the matter wave of a single-photon, has not yet been
entirely revealed. In this paper, we investigate the effect of dispersion on
indistinguishability of single-photon wave-packets through the Hong-Ou-Mandel
(HOM) interference. By dispersively manipulating two indistinguishable
single-photon wave-packets before interfering with each other, we observe that
the difference of the second-order dispersion between two optical paths of the
HOM interferometer can be mapped to the interference curve, indicating that (1)
with the same amount of dispersion effect in both paths, the HOM interference
curve must be only determined by the intrinsic indistinguishability between the
wave-packets, i.e., dispersion cancellation due to the indistinguishability
between Feynman paths; (2) unbalanced dispersion effect in two paths cannot be
cancelled and will broaden the interference curve thus providing a way to
measure the second-order dispersion coefficient. Our results suggest a more
comprehensive understanding of the single-photon wave-packet and pave ways to
explore further applications of the HOM interference
- …