5,169 research outputs found
Automated tracking of colloidal clusters with sub-pixel accuracy and precision
Quantitative tracking of features from video images is a basic technique
employed in many areas of science. Here, we present a method for the tracking
of features that partially overlap, in order to be able to track so-called
colloidal molecules. Our approach implements two improvements into existing
particle tracking algorithms. Firstly, we use the history of previously
identified feature locations to successfully find their positions in
consecutive frames. Secondly, we present a framework for non-linear
least-squares fitting to summed radial model functions and analyze the accuracy
(bias) and precision (random error) of the method on artificial data. We find
that our tracking algorithm correctly identifies overlapping features with an
accuracy below 0.2% of the feature radius and a precision of 0.1 to 0.01 pixels
for a typical image of a colloidal cluster. Finally, we use our method to
extract the three-dimensional diffusion tensor from the Brownian motion of
colloidal dimers.Comment: 20 pages, 8 figures. Non-revised preprint version, please refer to
http://dx.doi.org/10.1088/1361-648X/29/4/04400
Microparticle assembly pathways on lipid membranes
Understanding interactions between microparticles and lipid membranes is of
increasing importance, especially for unraveling the influence of microplastics
on our health and environment. Here, we study how a short-ranged adhesive force
between microparticles and model lipid membranes causes membrane-mediated
particle assembly. Using confocal microscopy, we observe the initial particle
attachment to the membrane, then particle wrapping, and in rare cases
spontaneous membrane tubulation. In the attached state, we measure that the
particle mobility decreases by 26%. If multiple particles adhere to the same
vesicle, their initial single-particle state determines their interactions and
subsequent assembly pathways: 1) attached particles only aggregate when small
adhesive vesicles are present in solution, 2) wrapped particles reversibly
attract one another by membrane deformation, and 3) a combination of wrapped
and attached particles form membrane-mediated dimers, which further assemble
into a variety of complex structures. The experimental observation of distinct
assembly pathways induced only by a short ranged membrane-particle adhesion,
shows that a cellular cytoskeleton or other active components are not required
for microparticle aggregation. We suggest that this membrane-mediated
microparticle aggregation is a reason behind reported long retention times of
polymer microparticles in organisms.Comment: 20 pages, 11 figures (including supporting material
On the Crossroads of History:Politics of History in Ukraine and Questions of identity in Post-Cold War Europe (1991 – 2019)
Since the inauspicious events of 2013-2014, Ukraine is in domestic and international turmoil. The Russian annexation of the Crimea was the first major act of its kind since the Second World War. Likewise, the downing of Malaysian Airlines flight MH17 shocked the world. The political consequences remain to this day. In all convolutions, domestic and foreign politicians often appealed to history. Conflicting perceptions of history are an essential element of the so-called ‘Ukraine Crisis’. This study demonstrates that political usage of history did not appear out of thin air. Ever since Ukraine became independent in 1991 politicians and historians sought to reinterpret the country’s complicated past. Inspired by nationalist ideology they tried to give Ukraine a national ‘European history’. To this, adherents of the old Soviet-style of Ukrainian history responded with vigour. Creating a tense political atmosphere wherein both sides polarized Ukrainian society around two extremes. Ukraine is not unique: since 1991, historians and politicians in Europe and Russia have also sought to redefine interpretations of history. While post-Communist Europe wanted to revaluate the meaning of communist and Nazi totalitarian rule, Western Europe sought to protect a narrative that sees Nazi crimes as the blackest page of history. On the other hand, Russia increasingly depends on presenting the Second World War as a great triumph. By contrasting the developments in Ukraine with other European and Russian experiences this study asks difficult but much-needed questions about what history means in our present
Bounds for the mean and standard deviation of linear combinations of order statistics : (preprint)
Pharmacologic management of the opioid neonatal abstinence syndrome.
Opioid use in pregnant women has increased over the last decade. Following birth, infants with in utero exposure demonstrate signs and symptoms of withdrawal known as the neonatal abstinence syndrome (NAS). Infants express a spectrum of disease, with most requiring the administration of pharmacologic therapy to ensure proper growth and development. Treatment often involves prolonged hospitalization. There is a general lack of high-quality clinical trial data to guide optimal therapy, and significant heterogeneity in treatment approaches. Emerging trends in the treatment of infants with NAS include the use of sublingual buprenorphine, transition to outpatient therapy, and pharmacogenetic risk stratification
The spin parameter of uniformly rotating compact stars
We study the dimensionless spin parameter of uniformly
rotating neutron stars and quark stars in general relativity. We show
numerically that the maximum value of the spin parameter of a neutron star
rotating at the Keplerian frequency is for a wide class
of realistic equations of state. This upper bound is insensitive to the mass of
the neutron star if the mass of the star is larger than about . On
the other hand, the spin parameter of a quark star modeled by the MIT bag model
can be larger than unity and does not have a universal upper bound. Its value
also depends strongly on the bag constant and the mass of the star.
Astrophysical implications of our finding will be discussed.Comment: Minor changes to match the published versio
Double and triple calix[4]arenis connected via the oxygen functions
New macrocyclic molecules are described containing two or three p-tert-butylcalix[4]arene subunits connected via their oxygen atoms. These macrocycles are available by two general methods which are capable of producing assemblies with bridges of varying rigidity and length
Single-machine scheduling with stepwise tardiness costs and release times
We study a scheduling problem that belongs to the yard operations component of the railroad planning problems, namely the hump sequencing problem. The scheduling problem is characterized as a single-machine problem with stepwise tardiness cost objectives. This is a new scheduling criterion which is also relevant in the context of traditional machine scheduling problems. We produce complexity results that characterize some cases of the problem as pseudo-polynomially solvable. For the difficult-to-solve cases of the problem, we develop mathematical programming formulations, and propose heuristic algorithms. We test the formulations and heuristic algorithms on randomly generated single-machine scheduling problems and real-life datasets for the hump sequencing problem. Our experiments show promising results for both sets of problems
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