759 research outputs found
Mid-Infrared Soliton and Raman Frequency Comb Generation in Silicon Microrings
We numerically study the mechanisms of frequency comb generation in the
mid-infrared spectral region from cw pumped silicon microring resonators.
Coherent soliton comb generation may be obtained even for a pump with zero
linear cavity detuning, through suitable control of the effective lifetime of
free-carriers from multiphoton absorption, which introduces a nonlinear cavity
detuning via free-carrier dispersion. Conditions for optimal octave spanning
Raman comb generation are also described
Dynamics of microresonator frequency comb generation: models and stability
Microresonator frequency combs hold promise
for enabling a new class of light sources that are simultaneously
both broadband and coherent, and that could
allow for a profusion of potential applications. In this article,
we review various theoretical models for describing
the temporal dynamics and formation of optical frequency
combs. These models form the basis for performing numerical
simulations that can be used in order to better understand
the comb generation process, for example helping to
identify the universal combcharacteristics and their different
associated physical phenomena. Moreover, models allow
for the study, design and optimization of comb properties
prior to the fabrication of actual devices. We consider
and derive theoretical formalisms based on the Ikeda map,
the modal expansion approach, and the Lugiato-Lefever
equation. We further discuss the generation of frequency
combs in silicon resonators featuring multiphoton absorption
and free-carrier effects. Additionally, we review comb
stability properties and consider the role of modulational
instability as well as of parametric instabilities due to the
boundary conditions of the cavity. These instability mechanisms
are the basis for comprehending the process of frequency
comb formation, for identifying the different dynamical
regimes and the associated dependence on the
comb parameters. Finally, we also discuss the phenomena
of continuous wave bi- and multistability and its relation
to the observation of mode-locked cavity solitons
Dynamics of microresonator frequency comb generation: models and stability
Microresonator frequency combs hold promise
for enabling a new class of light sources that are simultaneously
both broadband and coherent, and that could
allow for a profusion of potential applications. In this article,
we review various theoretical models for describing
the temporal dynamics and formation of optical frequency
combs. These models form the basis for performing numerical
simulations that can be used in order to better understand
the comb generation process, for example helping to
identify the universal combcharacteristics and their different
associated physical phenomena. Moreover, models allow
for the study, design and optimization of comb properties
prior to the fabrication of actual devices. We consider
and derive theoretical formalisms based on the Ikeda map,
the modal expansion approach, and the Lugiato-Lefever
equation. We further discuss the generation of frequency
combs in silicon resonators featuring multiphoton absorption
and free-carrier effects. Additionally, we review comb
stability properties and consider the role of modulational
instability as well as of parametric instabilities due to the
boundary conditions of the cavity. These instability mechanisms
are the basis for comprehending the process of frequency
comb formation, for identifying the different dynamical
regimes and the associated dependence on the
comb parameters. Finally, we also discuss the phenomena
of continuous wave bi- and multistability and its relation
to the observation of mode-locked cavity solitons
Differential Proteome Analysis of the Preeclamptic Placenta Using Optimized Protein Extraction
The human placenta is a difficult tissue to work with using proteomic technology since it contains large amounts of lipids and glycogen. Both lipids and glycogen are known to interfere with the first step in the two-dimensional polyacrylamide gel electrophoresis (2D-PAGE), the isoelectric focusing. In order to gain the best possible protein separation on 2D-PAGE, an optimized sample preparation protocol for placental proteins was developed. Two different buffers, urea/CHAPS and Hepes, were used for solubilization in combination with six different precipitation methods. The removal of glycogen from the samples by centrifugation was crucial for the final proteome maps. Solubilization with urea/CHAPS in combination with dichloromethane/methanol or acidified acetone proved to be the best precipitation procedures. When applied to clinical placenta samples apolipoprotein A1 was found to be accumulated in the preeclamptic placenta, where it may either have a nutritional effect or act as a modifier of signal transduction
Control of Kerr Cavity Soliton Combs by Chirped Pumping
Pumping a dispersive Kerr cavity with chirped pump pulses permits to control the trapping position of temporal cavity soliton combs. Stability of single-cavity soliton generation is greatly enhanced by pump chirping
Novel generation schemes for stable soliton states in optical microcavities
The excitation of Kerr optical frequency combs(OFC) is frequently non-deterministic and remains a cumbersome problem in many practical situations. While standard techniques to generate Kerr solitons in passive resonators employ a continuous wave pump, recently pulsed pumping has also been proposed. In this study we individuate and classify OFC states in a phase space defined by an experimental set of coordinates and triggered by a general super-Gaussian chirped driving field. Our numerical analysis shows how the soliton drifts caused by the phase modulation of the input field accelerate the dynamics and convergence towards a stable soliton stat
Vacuum-assisted wound closure versus alginate for the treatment of deep perivascular wound infections in the groin after vascular surgery
BackgroundVacuum-assisted wound closure (VAC) therapy may heal wounds faster than conventional dressings after surgical debridement of perivascular groin infections after vascular surgery.MethodsPatients with deep infected wounds (Szilagyi grade III) were surgically revised and left open for secondary healing, then randomized to either VAC or alginate (Sorbalgon) therapy, between February 2007 and November 2011. To test the hypothesis, it was calculated that 42 patients needed to be included (90% power, 5% level of significance). It was decided to perform an interim analysis after inclusion of 20 patients.ResultsAmong 66 patients undergoing groin revision, 20 patients were included in this study. Patients were randomized to VAC (n = 10) or alginate (n = 10). The two groups were comparable in patient and wound characteristics. Time to full skin epithelialization was significantly shorter in the VAC group (median, 57 days) compared with the alginate group (median, 104 days; P = .026). The number of positive wound cultures of bacteria and C-reactive protein values decreased equally in both groups between surgical revision and day 21. One femur amputation was performed in each group as a consequence of the groin infection, one patient died during the in-hospital stay in the alginate group, and none died in the VAC group.ConclusionsVAC achieves faster healing than alginate therapy after wound debridement for deep perivascular wound infections in the groin after vascular surgery. This finding does not allow further inclusion of patients from an ethical point of view, and this study was, therefore, stopped prematurely
Nonlinear beam self-imaging and self-focusing dynamics in a GRIN multimode optical fiber: theory and experiments
Beam self-imaging in nonlinear graded-index multimode optical fibers is of
interest for many applications, such as implementing a fast saturable absorber
mechanism in fiber lasers via multimode interference. We obtain an exact
solution for the nonlinear evolution of first and second order moments of a
laser beam carried by a graded-index multimode fiber, predicting that the
spatial self-imaging period does not vary with power. Whereas the amplitude of
the oscillation of the beam width is power-dependent. We have experimentally
studied the longitudinal evolution of beam self-imaging by means of femtosecond
laser pulse propagation in both the anomalous and the normal dispersion regime
of a standard telecom graded-index multimode optical fiber. Light scattering
out of the fiber core via visible fluorescence emission and harmonic wave
generation permits us to directly confirm that the self-imaging period is
invariant with power. Spatial shift and splitting of the self-imaging process
under the action of self-focusing are also emphasized
Organic Cultivation of Lemon Ballm (Melissa officinalis) in Macedonia
The possibility for perspective growing of medicinal, aromatic and spice plants, can be expected only if their cultivation is
based on the principles of organic farming. The cultivation of this group of plants is usually associated with satisfactory yield level
and raw materials with uniform quality. This paper contains the most important features of lemon balm (Melissa officinalis), and
methods of cultivation. Data of two annual activities are presented and they are related with organic system of cultivation in the
central part of Macedonia. The objective of this study is to analyze, determine and demonstrate the economic viability of lemon balm
organic production with irrigation. In the first year, there were only two moving, yielding 500 kg/ha of above-ground plant dry mass.
In the second year, there were three moving, yielding 6,775 kg/ha of above-ground plant dry mass. Economic analysis is proved that
profitability in organically produced lemon balm is obtained in the second year of growing when the profit reached $6,150/ha.
Key words: Organic, lemon balm, yield, pofitability
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