12,644 research outputs found
Brownian motion in a non-homogeneous force field and photonic force microscope
The Photonic Force Microscope (PFM) is an opto-mechanical technique based on
an optical trap that can be assumed to probe forces in microscopic systems.
This technique has been used to measure forces in the range of pico- and
femto-Newton, assessing the mechanical properties of biomolecules as well as of
other microscopic systems. For a correct use of the PFM, the force field to
measure has to be invariable (homogeneous) on the scale of the Brownian motion
of the trapped probe. This condition implicates that the force field must be
conservative, excluding the possibility of a rotational component. However,
there are cases where these assumptions are not fulfilled Here, we show how to
improve the PFM technique in order to be able to deal with these cases. We
introduce the theory of this enhanced PFM and we propose a concrete analysis
workflow to reconstruct the force field from the experimental time-series of
the probe position. Furthermore, we experimentally verify some particularly
important cases, namely the case of a conservative or rotational force-field
The buyer margins of firms' exports
We use highly disaggregated firm-level export data from Costa Rica, Ecuador, and Uruguay over the period 2005-2008 to provide a precise characterization of firms' export margins, across products, destination countries, and crucially customers. We show that a firm's number of buyers and the distribution of sales across them systematically vary with the characteristics of its destination markets. While most firms serve only very few buyers abroad, the number of buyers and the skewness of sales across them increases with the size and the accessibility of destinations. We develop a simple model of selection with heterogeneous buyers and sellers consistent with these findings in which tougher competition induces a better alignment between consumers' ideal variants and firms' core competencies. This generates an additional channel through which tougher competition leads to higher productivity and higher welfare and hints at an additional source of gains from trade as long as freer trade fosters competition
SMEs in Argentina: Who are the Exporters?
There exists a growing body of literature which looks at export decisions made by firms. Most studies focus on developed countries and do not explore whether different behavioral patterns prevail over the firm size distribution. This paper aims at filling this gap in the literature by analyzing the export behavior of a statistically representative sample of 192 Small and Medium-Size Enterprises (SMEs) in a developing country, Argentina, over the period 1996-1998. We find that the level of employment, sourcing from abroad, investment in product improvement and average productivity are associated with a higher probability of exporting. Training activities for employees are important to export outside of MERCOSUR.SME, Exports, Argentina
Experimental and numerical study of error fields in the CNT stellarator
Sources of error fields were indirectly inferred in a stellarator by
reconciling computed and numerical flux surfaces. Sources considered so far
include the displacements and tilts (but not the deformations, yet) of the four
circular coils featured in the simple CNT stellarator. The flux surfaces were
measured by means of an electron beam and phosphor rod, and were computed by
means of a Biot-Savart field-line tracing code. If the ideal coil locations and
orientations are used in the computation, agreement with measurements is poor.
Discrepancies are ascribed to errors in the positioning and orientation of the
in-vessel interlocked coils. To that end, an iterative numerical method was
developed. A Newton-Raphson algorithm searches for the coils' displacements and
tilts that minimize the discrepancy between the measured and computed flux
surfaces. This method was verified by misplacing and tilting the coils in a
numerical model of CNT, calculating the flux surfaces that they generated, and
testing the algorithm's ability to deduce the coils' displacements and tilts.
Subsequently, the numerical method was applied to the experimental data,
arriving at a set of coil displacements whose resulting field errors exhibited
significantly improved quantitative and qualitative agreement with experimental
results.Comment: Special Issue on the 20th International Stellarator-Heliotron
Worksho
Molecular adaptation to calsequestrin 2 (CASQ2) point mutations leading to catecholaminergic polymorphic ventricular tachycardia (CPVT): comparative analysis of R33Q and D307H mutants
Homozygous calsequestrin 2 (CASQ2) point mutations leads to catecholaminergic polymorphic ventricular tachycardia: a common pathogenetic feature appears to be the drastic reduction of mutant CASQ2 in spite of normal transcription. Comparative biochemical analysis of R33Q and D307H knock in mutant mice identifies different pathogenetic mechanisms for CASQ2 degradation and different molecular adaptive mechanisms. In particular, each CASQ2 point mutation evokes specific adaptive cellular and molecular processes in each of the four adaptive pathways investigated. Thus, similar clinical phenotypes and identical cellular mechanism for cardiac arrhythmia might imply different molecular adaptive mechanisms
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