5,519 research outputs found
Cannibalism as a life boat mechanism
Under certain conditions a cannibalistic population can survive when food for the adults is too scarce to support a non-cannibalistic population. Cannibalism can have this lifeboat effect if (i) the juveniles feed on a resource inaccessible to the adults; and (ii) the adults are cannibalistic and thus incorporate indirectly the inaccessible resource. Using a simple model we conclude that the mechanism works when, at low population densities, the average yield, in terms of new offspring, due to the energy provided by one cannibalized juvenile is larger than one
Preferred Measurements: Optimality and Stability in Quantum Parameter Estimation
We explore precision in a measurement process incorporating pure probe
states, unitary dynamics and complete measurements via a simple formalism. The
concept of `information complement' is introduced. It undermines measurement
precision and its minimization reveals the system properties at an optimal
point. Maximally precise measurements can exhibit independence from the true
value of the estimated parameter, but demanding this severely restricts the
type of viable probe and dynamics, including the requirement that the
Hamiltonian be block-diagonal in a basis of preferred measurements. The
curvature of the information complement near a globally optimal point provides
a new quantification of measurement stability.Comment: 4 pages, 2 figures, in submission. Substantial Extension and
replacement of arXiv:0902.3260v1 in response to Referees' remark
Entanglement of four qubit systems: a geometric atlas with polynomial compass I (the finite world)
We investigate the geometry of the four qubit systems by means of algebraic
geometry and invariant theory, which allows us to interpret certain entangled
states as algebraic varieties. More precisely we describe the nullcone, i.e.,
the set of states annihilated by all invariant polynomials, and also the so
called third secant variety, which can be interpreted as the generalization of
GHZ-states for more than three qubits. All our geometric descriptions go along
with algorithms which allow us to identify any given state in the nullcone or
in the third secant variety as a point of one of the 47 varieties described in
the paper. These 47 varieties correspond to 47 non-equivalent entanglement
patterns, which reduce to 15 different classes if we allow permutations of the
qubits.Comment: 48 pages, 7 tables, 13 figures, references and remarks added (v2
COMPARATIVE ASSESSMENT OF CARBON STORAGE IN BIOMASS AND SOIL ORGANIC CARBON IN TEAK PLANTATION OF DIFFERENT AGES IN YEWA NORTH, OGUN STATE, NIGERIA
Tree act as a sink for CO2 by fixing carbon during photosynthesis and is a vital tool to alleviate climate change through CO2 absorption from the atmosphere. This study was conducted to assess carbon storage in tree biomass and soil carbon stock in Teak (Tectona grandis) plantations of different age series (5, 9 and 12 years). Data were collected on diameter at breast height (Dbh) and total height (TH) of all the trees in a sample plot of 1000 m2 in each plantation of age series. Carbon stored was evaluated based on tree growth variables, soil parameters and above ground biomass. Topsoil and subsoil (0-15 and 15-30 cm) samples collected from three sites were analyzed for organic carbon (OC) following standard methods. Mean diameter at breast height were 67.11, 45.42, and 21.35 cm ha-1 and the mean volumes were 0.39, 0.16 and 0.02 m3ha-1 for 12, 9 and 5 years old were significant different (p<0.05). The highest value of total soil organic carbon (TSOC) was 8464.65 t.ha-1 for the 12year-old followed by 4430.25 t.ha-1 for 9 years old stand and 3004.95 t.ha-1 for 5years old were significant different (p<0.05) respectively. The total soil organic carbon per hectare were higher for the older than the younger Tectona grandis stand (8464.65 t.ha-1, 4430.25 t.ha-1 and 3004.95 t.ha-1) were significant different (p<0.05). Total carbon storage by soil and in biomass (CSB) was 15899.85 and 49.31 tons.ha-1 and total carbon accumulated by the plantation under investigation was in the order of 12 years old > 9 years old > 5 years old, respectively. The results of this study confirm that teak has good potentials to offer carbon sequestration through its soil and accumulate large amount of biomass carbon. The plantation ownership should be guided properly on the management activities such as thinning, pruning and weeding operation as well as indiscriminate removal of individual caused by anthropogenic activities should be avoided.
 
Lorentz invariance of entanglement classes in multipartite systems
We analyze multipartite entanglement in systems of spin-1/2 particles from a
relativistic perspective. General conditions which have to be met for any
classification of multipartite entanglement to be Lorentz invariant are
derived, which contributes to a physical understanding of entanglement
classification. We show that quantum information in a relativistic setting
requires the partition of the Hilbert space into particles to be taken
seriously. Furthermore, we study exemplary cases and show how the spin and
momentum entanglement transforms relativistically in a multipartite setting.Comment: v2: 5 pages, 4 figures, minor changes to main body, journal
references update
Torsion nonminimally coupled to the electromagnetic field and birefringence
In conventional Maxwell--Lorentz electrodynamics, the propagation of light is
influenced by the metric, not, however, by the possible presence of a torsion
T. Still the light can feel torsion if the latter is coupled nonminimally to
the electromagnetic field F by means of a supplementary Lagrangian of the type
l^2 T^2 F^2 (l = coupling constant). Recently Preuss suggested a specific
nonminimal term of this nature. We evaluate the spacetime relation of Preuss in
the background of a general O(3)-symmetric torsion field and prove by
specifying the optical metric of spacetime that this can yield birefringence in
vacuum. Moreover, we show that the nonminimally coupled homogeneous and
isotropic torsion field in a Friedmann cosmos affects the speed of light.Comment: Revtex, 12 pages, no figure
Surgical management and longterm follow-up of non-parasitic hepatic cysts
BACKGROUND: Despite the increasing use of laparoscopic techniques, the optimal surgical approach for cystic liver disease has not been well defined. This study aims to determine the optimum operative approach for these patients. METHODS: Data were identified from the Lothian Surgical Audit, case note review and general practitioner contact. Patients were contacted and asked to complete the SF-36 questionnaire on quality of life. RESULTS: A total of 102 patients (67 with simple cysts, 31 with polycystic liver disease [PCLD], four with cystic tumours) underwent 62 laparoscopic deroofings, 15 open deroofings, 36 resections and one liver transplant between June 1985 and April 2006. The median follow-up was 77 months (range 3â250 months). Morbidity and recurrent symptom rates after laparoscopic surgery were greater in PCLD patients compared with simple cyst patients, at 31% (four patients) vs. 15% (seven patients) and 85% (11 patients) vs. 29% (24 patients), respectively. Four patients with simple cysts and eight with PCLD required further surgery. All patients with simple cysts had comparable quality of life after surgery. Patients with recurrent symptoms after surgery for PCLD had a significantly better quality of life following laparoscopic deroofing than after resection. CONCLUSIONS: Most simple cysts can be managed laparoscopically, but there is a definite role for open resection in some patients. Open deroofing is the preferred approach for a dominant cyst pattern in PCLD, whereas resection is necessary for diffuse cystic disease
Dissipative quantum chaos: transition from wave packet collapse to explosion
Using the quantum trajectories approach we study the quantum dynamics of a
dissipative chaotic system described by the Zaslavsky map. For strong
dissipation the quantum wave function in the phase space collapses onto a
compact packet which follows classical chaotic dynamics and whose area is
proportional to the Planck constant. At weak dissipation the exponential
instability of quantum dynamics on the Ehrenfest time scale dominates and leads
to wave packet explosion. The transition from collapse to explosion takes place
when the dissipation time scale exceeds the Ehrenfest time. For integrable
nonlinear dynamics the explosion practically disappears leaving place to
collapse.Comment: 4 pages, 4 figure
Observation and Modeling of the Solar Transition Region: II. Solutions of the Quasi-Static Loop Model
In the present work we undertake a study of the quasi-static loop model and
the observational consequences of the various solutions found. We obtain the
most general solutions consistent with certain initial conditions. Great care
is exercised in choosing these conditions to be physically plausible (motivated
by observations). We show that the assumptions of previous quasi-static loop
models, such as the models of Rosner, Tucker and Vaiana (1978) and Veseckey,
Antiochos and Underwood (1979), are not necessarily valid for small loops at
transition region temperatures. We find three general classes of solutions for
the quasi-static loop model, which we denote, radiation dominated loops,
conduction dominated loops and classical loops. These solutions are then
compared with observations. Departures from the classical scaling law of RTV
are found for the solutions obtained. It is shown that loops of the type that
we model here can make a significant contribution to lower transition region
emission via thermal conduction from the upper transition region.Comment: 30 pages, 3 figures, Submitted to ApJ, Microsoft Word File 6.0/9
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