867 research outputs found
Photophysics of single nitrogen-vacancy centers in diamond nanocrystals
A study of the photophysical properties of nitrogen-vacancy (NV) color
centers in diamond nanocrystals of size of 50~nm or below is carried out by
means of second-order time-intensity photon correlation and cross-correlation
measurements as a function of the excitation power for both pure charge states,
neutral and negatively charged, as well as for the photochromic state, where
the center switches between both states at any power. A dedicated three-level
model implying a shelving level is developed to extract the relevant
photophysical parameters coupling all three levels. Our analysis confirms the
very existence of the shelving level for the neutral NV center. It is found
that it plays a negligible role on the photophysics of this center, whereas it
is responsible for an increasing photon bunching behavior of the negative NV
center with increasing power. From the photophysical parameters, we infer a
quantum efficiency for both centers, showing that it remains close to unity for
the neutral center over the entire power range, whereas it drops with
increasing power from near unity to approximately 0.5 for the negative center.
The photophysics of the photochromic center reveals a rich phenomenology that
is to a large extent dominated by that of the negative state, in agreement with
the excess charge release of the negative center being much slower than the
photon emission process
Near-field microscopy with a scanning nitrogen-vacancy color center in a diamond nanocrystal: A brief review
We review our recent developments of near-field scanning optical microscopy
(NSOM) that uses an active tip made of a single fluorescent nanodiamond (ND)
grafted onto the apex of a substrate fiber tip. The ND hosting a limited number
of nitrogen-vacancy (NV) color centers, such a tip is a scanning quantum source
of light. The method for preparing the ND-based tips and their basic properties
are summarized. Then we discuss theoretically the concept of spatial resolution
that is achievable in this special NSOM configuration and find it to be only
limited by the scan height over the imaged system, in contrast with the
standard aperture-tip NSOM whose resolution depends critically on both the scan
height and aperture diameter. Finally, we describe a scheme we have introduced
recently for high-resolution imaging of nanoplasmonic structures with ND-based
tips that is capable of approaching the ultimate resolution anticipated by
theory.Comment: AD, AC, OM, MB and SH wish to dedicate this brief review article to
their co-author and colleague Yannick Sonnefraud who passed away in September
2014. Yannick initiated this research in 200
Interview Erwin Muller en Werner Overdijk
Erwin Muller en Werner Overdijk zijn beide werkzaam bij het Crisis Onderzoek Team, dat verbonden is aan de vakgroep bestuurskunde Rotterdam/Leiden. In dit artikel willen wij jullie nader kennis laten maken met hen en met het Crisis Onderzoek Team
Predicting performance of constant flow depth filtration using constant pressure filtration data
This paper describes a method of predicting constant flow filtration capacities using constant pressure datasets collected during the purification of several monoclonal antibodies through depth filtration. The method required characterisation of the fouling mechanism occurring in constant pressure filtration processes by evaluating the best fit of each of the classic and combined theoretical fouling models. The optimised coefficients of the various models were correlated with the corresponding capacities achieved during constant flow operation at the specific pressures performed during constant pressure operation for each centrate. Of the classic and combined fouling models investigated, the Cake-Adsorption fouling model was found to best describe the fouling mechanisms observed for each centrate at the various different pressures investigated. A linear regression model was generated with these coefficients and was shown to predict accurately the capacities at constant flow operation at each pressure. This model was subsequently validated using an additional centrate and accurately predicted the constant flow capacities at three different pressures (0.69, 1.03 and 1.38 bar). The model used the optimised Cake-Adsorption model coefficients that best described the flux decline during constant pressure operation. The proposed method of predicting depth filtration performance proved to be faster than the traditional approach whilst requiring significantly less material, making it particularly attractive for early process development activities
Cell sorting in a Petri dish controlled by computer vision.
Fluorescence-activated cell sorting (FACS) applying flow
cytometry to separate cells on a molecular basis is a widespread
method. We demonstrate that both fluorescent and unlabeled live
cells in a Petri dish observed with a microscope can be
automatically recognized by computer vision and picked up by a
computer-controlled micropipette. This method can be routinely
applied as a FACS down to the single cell level with a very
high selectivity. Sorting resolution, i.e., the minimum distance
between two cells from which one could be selectively removed
was 50-70 micrometers. Survival rate with a low number of 3T3
mouse fibroblasts and NE-4C neuroectodermal mouse stem cells was
66 +/- 12% and 88 +/- 16%, respectively. Purity of sorted
cultures and rate of survival using NE-4C/NE-GFP-4C co-cultures
were 95 +/- 2% and 62 +/- 7%, respectively. Hydrodynamic
simulations confirmed the experimental sorting efficiency and a
cell damage risk similar to that of normal FACS
ANALISIS EFEKTIFITAS DAN KONTRIBUSI HASIL PENGELOLAAN KEKAYAAN DAERAH YANG DIPISAHKAN TERHADAP PENDAPATAN ASLI DAERAH (PAD) PROVINSI PAPUA
The purpose of this research is to find and analyze how much the effectiveness of the local asset management and all that will be conducted in order to raise local revenue. Data used is secondary data. Analysis technique using the ratio of effectiveness and the ratio of contribution.
The result shows the ratio of effectiveness and the ratio of contributed to local revenue show a fairly good measurement, this can be seen from the the percentage value.
Keywords: effectiveness, contribution, local revenue
ANALISIS EFEKTIFITAS DAN KONTRIBUSI HASIL PENGELOLAAN KEKAYAAN DAERAH YANG DIPISAHKAN TERHADAP PENDAPATAN ASLI DAERAH (PAD) PROVINSI PAPUA
The purpose of this research is to find and analyze how much the effectiveness of the local asset management and all that will be conducted in order to raise local revenue. Data used is secondary data. Analysis technique using the ratio of effectiveness and the ratio of contribution.
The result shows the ratio of effectiveness and the ratio of contributed to local revenue show a fairly good measurement, this can be seen from the the percentage value.
Keywords: effectiveness, contribution, local revenue
A scale-down mimic for mapping the process performance of centrifugation, depth and sterile filtration
In the production of biopharmaceuticals disk-stack centrifugation is widely used as a harvest step for the removal of cells and cellular debris. Depth filters followed by sterile filters are often then employed to remove residual solids remaining in the centrate. Process development of centrifugation is usually conducted at pilot-scale so as to mimic the commercial scale equipment but this method requires large quantities of cell culture and significant levels of effort for successful characterization. A scale-down approach based upon the use of a shear device and a bench-top centrifuge has been extended in this work towards a preparative methodology that successfully predicts the performance of the continuous centrifuge and polishing filters. The use of this methodology allows the effects of cell culture conditions and large-scale centrifugal process parameters on subsequent filtration performance to be assessed at an early stage of process development where material availability is limited
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