638 research outputs found
Fast bias inversion of a double well without residual particle excitation
We design fast bias inversions of an asymmetric double well so that the
lowest states in each well remain so and free from residual motional
excitation. This cannot be done adiabatically, and a sudden bias switch
produces in general motional excitation. The residual excitation is suppressed
by complementing a predetermined fast bias change with a linear ramp whose
time-dependent slope compensates for the displacement of the wells. The
process, combined with vibrational multiplexing and demultiplexing, can produce
vibrational state inversion without exciting internal states, just by deforming
the trap.Comment: 7 pages, 6 figure
Charge transport in poly(dG)-poly(dC) and poly(dA)-poly(dT) DNA polymers
We investigate the charge transport in synthetic DNA polymers built up from
single types of base pairs. In the context of a polaron-like model, for which
an electronic tight-binding system and bond vibrations of the double helix are
coupled, we present estimates for the electron-vibration coupling strengths
utilizing a quantum-chemical procedure. Subsequent studies concerning the
mobility of polaron solutions, representing the state of a localized charge in
unison with its associated helix deformation, show that the system for
poly(dG)-poly(dC) and poly(dA)-poly(dT) DNA polymers, respectively possess
quantitatively distinct transport properties. While the former supports
unidirectionally moving electron breathers attributed to highly efficient
long-range conductivity the breather mobility in the latter case is
comparatively restrained inhibiting charge transport. Our results are in
agreement with recent experimental results demonstrating that poly(dG)-poly(dC)
DNA molecules acts as a semiconducting nanowire and exhibits better conductance
than poly(dA)-poly(dT) ones.Comment: 11 pages, 5 figure
Fast driving between arbitrary states of a quantum particle by trap deformation
By performing a slow adiabatic change between two traps of a quantum
particle, it is possible to transform an eigenstate of the original trap into
the corresponding eigenstate of the final trap. If no level crossings are
involved, the process can be made faster than adiabatic by setting first the
interpolated evolution of the wave function from its initial to its final form
and inferring from this evolution the trap deformation. We find a simple and
compact formula which gives the trap shape at any time for any interpolation
scheme. It is applicable even in complicated scenarios where there is no
adiabatic process for the desired state-transformation, e.g., if the state
changes its topological properties. We illustrate its use for the expansion of
a harmonic trap, for the transformation of a harmonic trap into a linear trap
and into an arbitrary number of traps of a periodic structure. Finally, we
study the creation of a node exemplified by the passage from the ground state
to the first excited state of a harmonic oscillator.Comment: 6 pages, 5 figure
Shortcuts to adiabaticity for an ion in a rotating radially-tight trap
We engineer the fast rotation of a quantum particle confined in an
effectively one-dimensional, harmonic trap, for a predetermined rotation angle
and time, avoiding final excitation. Different schemes are proposed with
different speed limits that depend on the control capabilities. We also make
use of trap rotations to create squeezed states without manipulating the trap
frequencies.Comment: 11 pages, 6 figure
Separation of particles leading to decay and unlimited growth of energy in a driven stadium-like billiard
A competition between decay and growth of energy in a time-dependent stadium
billiard is discussed giving emphasis in the decay of energy mechanism. A
critical resonance velocity is identified for causing of separation between
ensembles of high and low energy and a statistical investigation is made using
ensembles of initial conditions both above and below the resonance velocity.
For high initial velocity, Fermi acceleration is inherent in the system.
However for low initial velocity, the resonance allies with stickiness hold the
particles in a regular or quasi-regular regime near the fixed points,
preventing them from exhibiting Fermi acceleration. Also, a transport analysis
along the velocity axis is discussed to quantify the competition of growth and
decay of energy and making use distributions of histograms of frequency, and we
set that the causes of the decay of energy are due to the capture of the orbits
by the resonant fixed points
Comunicación corta. Rhizoctonia solani, agente causal de la muerte de plántulas de acelga en España
During September 2011, post-emergence damping off of Swiss chard (Beta vulgaris subsp. cicla L.) was observed in a greenhouse in Villa del Prado (Spain). About 20% of the seedlings showed damping off symptoms. Lesions were initially water soaked, dark brown necrosis of crown tissue, irregular in shape and sunken in appearance on large plants, causing the infected seedlings to collapse and eventually die. Rhizoctonia solani was isolated consistently from symptomatic plants. After morphological and molecular identification of the isolates, pathogenicity was tested by placing agar plugs of four isolates adjacent to the stem at the three or four true leaf stage. In inoculated plants, brown crown and stem necrosis occurred while control plants did not show disease symptoms. Pathogenicity using non-germinated seeds was also tested. All four isolates produced extensive damping off when inoculated on non-germinated seeds. To our knowledge, this is the first report of damping off of Swiss chard caused by R. solani in Europe.En el mes de septiembre de 2011, se observĂł muerte de plántulas en acelgas cultivadas en un invernadero en Villa del Prado (España). Cerca del 20% de los semilleros mostraban sĂntomas de caĂda de plántulas. Las lesiones iniciales tenĂan un aspecto hĂşmedo y consistĂan en una necrosis del tejido de la corona de color marrĂłn oscuro, de bordes irregulares y deprimidos en las plantas adultas, produciendo el colapso de las plántulas y, ocasionalmente, la muerte de las mismas. Rhizoctonia solani se aislĂł de manera consistente de las plantas sintomáticas. Tras una identificaciĂłn morfolĂłgica y molecular, la patogenicidad de los aislados se probĂł colocando discos de agar adyacentes al tallo de la planta en estados de tres o cuatro hojas verdaderas. En las plantas inoculadas se observĂł un oscurecimiento de la corona y la necrosis del tallo en todos los casos, sĂntomas que no mostraron las plantas control. Por otro lado, se comprobĂł la patogenicidad de los aislados en semillas no germinadas. Los cuatro aislados produjeron muerte de plántulas cuando se inocularon en semillas no germinadas. Hasta donde hemos podido comprobar, este trabajo parece ser la primera cita de muerte de plántulas de acelga causada por R. solani en Europa
Fungal microbiota from rain water and pathogenicity of Fusarium species isolated from atmospheric dust and rainfall dust
In order to determine the presence of Fusarium spp. in atmospheric dust and rainfall dust, samples were collected during September 2007, and July, August, and October 2008. The results reveal the prevalence of airborne Fusarium species coming from the atmosphere of the South East coast of Spain. Five different Fusarium species were isolated from the settling dust: Fusarium oxysporum, F. solani, F. equiseti, F. dimerum, and F. proliferatum. Moreover, rainwater samples were obtained during significant rainfall events in January and February 2009. Using the dilution-plate method, 12 fungal genera were identified from these rainwater samples. Specific analyses of the rainwater revealed the presence of three species of Fusarium: F. oxysporum, F. proliferatum and F. equiseti. A total of 57 isolates of Fusarium spp. obtained from both rainwater and atmospheric rainfall dust sampling were inoculated onto melon (Cucumis melo L.) cv. Piñonet and tomato (Lycopersicon esculentum Mill.) cv. San Pedro. These species were chosen because they are the main herbaceous crops in Almeria province. The results presented in this work indicate strongly that spores or propagules of Fusarium are able to cross the continental barrier carried by winds from the Sahara (Africa) to crop or coastal lands in Europe. Results show differences in the pathogenicity of the isolates tested. Both hosts showed root rot when inoculated with different species of Fusarium, although fresh weight measurements did not bring any information about the pathogenicity. The findings presented above are strong indications that long-distance transmission of Fusarium propagules may occur. Diseases caused by species of Fusarium are common in these areas. They were in the past, and are still today, a problem for greenhouses crops in AlmerĂa, and many species have been listed as pathogens on agricultural crops in this region. Saharan air masses dominate the Mediterranean regions. The evidence of long distance dispersal of Fusarium spp. by atmospheric dust and rainwater together with their proved pathogenicity must be taken into account in epidemiological studies
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