11,513 research outputs found
Optical properties of charged quantum dots doped with a single magnetic impurity
We present a microscopic theory of the optical properties of self-assembled
quantum dots doped with a single magnetic manganese (Mn) impurity and
containing a controlled number of electrons. The single-particle electron and
heavy-hole electronic shells are described by two-dimensional harmonic
oscillators. The electron-electron, electron-hole Coulomb as well as the
short-range electron spin-Mn spin and hole spin-Mn spin contact exchange
interactions are included. The electronic states of the photo-excited
electron-hole-Mn complex and of the final electron-Mn complex are expanded in a
finite number of configurations and the full interacting Hamiltonian is
diagonalized numerically. The emission spectrum is predicted as a function of
photon energy for a given number of electrons and different number of confined
electronic quantum dot shells. We show how emission spectra allow to identify
the number of electronic shells, the number of electrons populating these
shells and, most importantly, their spin. We show that electrons not
interacting directly with the spin of Mn ion do so via electron-electron
interactions. This indirect interaction is a strong effect even when Mn
impurity is away from the quantum dot center.Comment: 12 pages, 10 figure
Mechanical Characterization of Torsional Micropaddles Using Atomic Force Microscopy
The reference cantilever method is shown to act as a direct and simple method for determination of torsional spring constant. It has been applied to the characterization of micropaddle structures similar to those proposed for resonant functionalized chemical sensors and resonant thermal detectors. It is shown that this method can be used as an effective procedure to characterize a key parameter of these devices and would be applicable to characterization of other similar MEMS/NEMS devices such as micromirrors. In this study, two sets of micropaddles are manufactured (beams at centre and offset by 2.5 ÎĽm) by using LPCVD silicon nitride as a substrate. The patterning is made by direct milling using focused ion beam. The torsional spring constant is achieved through micromechanical analysis via atomic force microscopy. To obtain the gradient of force curve, the area of the micropaddle is scanned and the behaviour of each pixel is investigated through an automated developed code. The experimental results are in a good agreement with theoretical results
Arp2/3 complex activity in filopodia of spreading cells
Background
Cells use filopodia to explore their environment and to form new adhesion contacts for motility and spreading. The Arp2/3 complex has been implicated in lamellipodial actin assembly as a major nucleator of new actin filaments in branched networks. The interplay between filopodial and lamellipodial protrusions is an area of much interest as it is thought to be a key determinant of how cells make motility choices.
Results
We find that Arp2/3 complex localises to dynamic puncta in filopodia as well as lamellipodia of spreading cells. Arp2/3 complex spots do not appear to depend on local adhesion or on microtubules for their localisation but their inclusion in filopodia or lamellipodia depends on the activity of the small GTPase Rac1. Arp2/3 complex spots in filopodia are capable of incorporating monomeric actin, suggesting the presence of available filament barbed ends for polymerisation. Arp2/3 complex in filopodia co-localises with lamellipodial proteins such as capping protein and cortactin. The dynamics of Arp2/3 complex puncta suggests that they are moving bi-directionally along the length of filopodia and that they may be regions of lamellipodial activity within the filopodia.
Conclusion
We suggest that filopodia of spreading cells have regions of lamellipodial activity and that this activity affects the morphology and movement of filopodia. Our work has implications for how we understand the interplay between lamellipodia and filopodia and for how actin networks are generated spatially in cells
Supersymmetrization of the Radiation Damping
We construct a supersymmetrized version of the model to the radiation damping
\cite{03} introduced by the present authors \cite{ACWF}. We dicuss its
symmetries and the corresponding conserved Noether charges. It is shown this
supersymmetric version provides a supersymmetric generalization of the Galilei
algebra obtained in \cite{ACWF}. We have shown that the supersymmetric action
can be splited into dynamically independent external and internal sectors.Comment: 9 page
Impact of inoculum size on mead aroma compounds formation by wine strains of S. cerevisiae
Mead is a traditional drink, containing 8-18% (v/v) of ethanol, which results from the alcoholic fermentation of diluted honey performed by yeasts. It has been reported that mead fermentation is a time-consuming process, and an important objective of mead makers is to reduce the fermentation time without decreasing the quality of the end product. A significant time can be saved in the fermentation process by increasing the pitching rate, i.e., the amount of suspended yeast cells added to a batch fermenter. However, an increase in the inoculum size could also have deleterious side effects on the flavour profile of the final beverage. Therefore, the aim of this study was to investigate the impact of the inoculum size of two commercial winemaking strains of Saccharomyces cerevisiae (Lalvin QA23 and Lalvin ICV D47) on the mead volatile aromatic compound production. Honey must was prepared according to the recipe developed by our team, supplemented with potassium tartrate, pH adjusted to 3.7 with malic acid and the nitrogen concentration adjusted to 267 mg/L with diammonium phosphate. The appropriate amounts of inoculum were pitched into the honey-must to obtain five different pitching rates. Mead produced was analysed for major volatile compounds by GC-FID and for minor volatile compounds by GC-MS. A total of twenty-seven fermentative aroma compounds including alcohols, esters, volatile phenols, volatile fatty acids and carbonyl compounds were identified and quantified in meads. It was observed quantitative differences in aroma profiles, confirming the contribution of both yeast strain and inoculum size on the sensory characteristics of meads. Of the twenty-seven volatile compounds quantified, fourteen could contribute to mead aroma and flavour because their concentrations rose above their respective thresholds. In general, the formation of these compounds was particularly pronounced at low pitching rates. The esters ethyl hexanoate, ethyl octanoate and isoamyl acetate were the most powerful odorants detected in all meads. In addition to this quantitative analysis of the impact of strain selection and inoculum size on mead aroma, a complementary sensorial evaluation of the meads would yield further useful information for mead producers
Effect of Saccharomyces cerevisiae cells immobilisation on mead production
Mead is a traditional alcoholic beverage obtained by the fermentation of diluted honey performed by yeasts. In this work the potential of application of immobilised yeast cells on single-layer Ca-alginate or
double-layer alginateechitosan for mead production was assessed for the first time. The meads produced either with entrapped or free cells were evaluated in terms of quality and aroma profile. The immobilisation
procedure had no adverse effect on cell viability, since minor differences were found in fermentation kinetics among the strains and immobilisation systems. The double-layer alginate-chitosan had no advantage compared with the single-layer Ca-alginate, as the number of free cells in the medium,
resulting from cell leakage, was similar. Although meads obtained with entrapped yeast cells presented less ethanol and glycerol and more acetic acid, it exhibited larger amounts of volatile compounds. Immobilised cells produced meads with more compounds with fruity characteristics, such as ethyl octanoate and ethyl hexanoate; however the concentrations of undesirable compounds in such meads were also higher. The effect of immobilisation on the aroma profile was important, but the strain
contribution was also of major importance. Thus, the sensory analysis of final product gives an important insight on the overall quality.The research presented in this paper was partially funded by the Fundacdo para a Ciencia e Tecnologia, (FCT) and by PTDC projects (contracts PTDC/AGR-ALI/68284/2006). A.P.P. is a recipient of a Ph.D. grant from the FCT (SFRH/BD/45820/2008)
Effect of nitrogen supplementation on yeast fermentation performance and mead quality
Mead is a traditional drink, containing X-1 X% (v/v) of ethanol, which results from the alcoholic fermentation of diluted honey performed by yeasts. However, when it is produced in a homemade way mead producers find several problems, namely, the lack of uniformity in the final products low or premature fermentations arrest, and
the production of "off-flavours" by the yeasts. These problems could be due to several factors, including lack of essential nutrients such as a deficiency in available nitrogen. Additionally , it has been reported that mead
fermentation is a time-consuming process, often taking several months to complete. depending on the type of
honey, yeast strain anti honey-must composition. Since mead production is a time-consuming process. to make
its production viable it is necessary to reduce the fermentation time while producing an end product of quality.
Thus. the aim of this study was to evaluate I he effect of nitrogen addition 10 honey-must on two active dry wine
yeasts (ADWY) fermentation performance, as well as on the mead composition and volatile aroma compounds
production
Dirac quantization of a nonminimal gauged O(3) sigma model
The (2+1) dimensional gauged O(3) nonlinear sigma model with Chern-Simons
term is canonically quantized. Furthermore, we study a nonminimal coupling in
this model implemented by means of a Pauli-type term. It is shown that the set
of constraints of the model is modified by the introduction of the Pauli
coupling. Moreover, we found that the quantum commutator relations in the
nominimal case is independent of the Chern-Simons coefficient, in contrast to
the minimal one.Comment: 7 pages, to appear in Modern Physics Letters
Avaliação de linhagens de arroz de terras altas no cerrado de Rondônia.
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