11,724 research outputs found
A unification in the theory of linearization of second order nonlinear ordinary differential equations
In this letter, we introduce a new generalized linearizing transformation
(GLT) for second order nonlinear ordinary differential equations (SNODEs). The
well known invertible point (IPT) and non-point transformations (NPT) can be
derived as sub-cases of the GLT. A wider class of nonlinear ODEs that cannot be
linearized through NPT and IPT can be linearized by this GLT. We also
illustrate how to construct GLTs and to identify the form of the linearizable
equations and propose a procedure to derive the general solution from this GLT
for the SNODEs. We demonstrate the theory with two examples which are of
contemporary interest.Comment: 8 page
First detection of CF+ towards a high-mass protostar
We report the first detection of the J = 1 - 0 (102.6 GHz) rotational lines
of CF+ (fluoromethylidynium ion) towards CygX-N63, a young and massive
protostar of the Cygnus X region. This detection occurred as part of an
unbiased spectral survey of this object in the 0.8-3 mm range, performed with
the IRAM 30m telescope. The data were analyzed using a local thermodynamical
equilibrium model (LTE model) and a population diagram in order to derive the
column density. The line velocity (-4 km s-1) and line width (1.6 km s-1)
indicate an origin from the collapsing envelope of the protostar.
We obtain a CF+ column density of 4.10e11 cm-2. The CF+ ion is thought to be
a good tracer for C+ and assuming a ratio of 10e-6 for CF+/C+, we derive a
total number of C+ of 1.2x10e53 within the beam. There is no evidence of carbon
ionization caused by an exterior source of UV photons suggesting that the
protostar itself is the source of ionization. Ionization from the protostellar
photosphere is not efficient enough. In contrast, X-ray ionization from the
accretion shock(s) and UV ionization from outflow shocks could provide a large
enough ionizing power to explain our CF+ detection.
Surprisingly, CF+ has been detected towards a cold, massive protostar with no
sign of an external photon dissociation region (PDR), which means that the only
possibility is the existence of a significant inner source of C+. This is an
important result that opens interesting perspectives to study the early
development of ionized regions and to approach the issue of the evolution of
the inner regions of collapsing envelopes of massive protostars. The existence
of high energy radiations early in the evolution of massive protostars also has
important implications for chemical evolution of dense collapsing gas and could
trigger peculiar chemistry and early formation of a hot core.Comment: 6 page
Argon assisted chemical vapor deposition of CrO: an efficient process leading to high quality epitaxial films
A comparative study of the structural, microstructural and magnetic
properties of CrO thin films grown onto (110) and (100) TiO rutile
single crystal substrates by chemical vapor deposition (CVD), using CrO as
chromium precursor and either oxygen or argon as carrier gas is presented. Our
results show that growth under argon carrier gas leads to high quality CrO
epilayers with structural and magnetic properties similar to those obtained
using the more standard oxygen carrier gas. Furthermore, we interpret the
larger magnetic coercivity observed for the (110) oriented films in terms of
their microstructure, in particular of the highest strain and edge roughness of
the building structures of the CrO epilayers, which are settled by the
substrate crystallographic orientation.Comment: 27 pages, 2 tables, 8 figure
Massive 70 micron quiet clumps I: evidence of embedded low/intermediate-mass star formation activity
Massive clumps, prior to the formation of any visible protostars, are the
best candidates to search for the elusive massive starless cores. In this work
we investigate the dust and gas properties of massive clumps selected to be 70
micron quiet, therefore good starless candidates. Our sample of 18 clumps has
masses 300 < M < 3000 M_sun, radius 0.54 < R < 1.00 pc, surface densities Sigma
> 0.05 g cm^-2 and luminosity/mass ratio L/M < 0.3. We show that half of these
70 micron quiet clumps embed faint 24 micron sources. Comparison with GLIMPSE
counterparts shows that 5 clumps embed young stars of intermediate stellar mass
up to ~5.5 M_sun. We study the clump dynamics with observations of N2H+ (1-0),
HNC (1-0) and HCO+ (1-0) made with the IRAM 30m telescope. Seven clumps have
blue-shifted spectra compatible with infall signatures, for which we estimate a
mass accretion rate 0.04 < M_dot < 2.0 x 10^-3 M_sun yr^-1, comparable with
values found in high-mass protostellar regions, and free-fall time of the order
of t_ff = 3 x 10^5 yr. The only appreciable difference we find between objects
with and without embedded 24 micron sources is that the infall rate appears to
increase from 24 micron dark to 24 micron bright objects. We conclude that all
70 micron quiet objects have similar properties on clump scales, independently
of the presence of an embedded protostar. Based on our data we speculate that
the majority, if not all of these clumps may already embed faint, low-mass
protostellar cores. If these clumps are to form massive stars, this must occur
after the formation of these lower mass stars.Comment: 44 pages, 11 Figures. Accepted for publication in MNRA
BEC-BCS crossover in a cold and magnetized two color NJL model
The BEC-BCS crossover for a NJL model with diquark interactions is studied in
the presence of an external magnetic field. Particular attention is paid to
different regularization schemes used in the literature. A thorough comparison
of results is performed for the case of a cold and magnetized two-color NJL
model. According to our results, the critical chemical potential for the BEC
transition exhibits a clear inverse magnetic catalysis effect for magnetic
fields in the range . As for the BEC-BCS
crossover, the corresponding critical chemical potential is very weakly
sensitive to magnetic fields up to , showing a much smaller
inverse magnetic catalysis as compared to the BEC transition, and displays a
strong magnetic catalysis from this point on.Comment: 15 pages, 8 figures; v2 PRD versio
On the distribution of high-frequency stock market traded volume: a dynamical scenario
This manuscript reports a stochastic dynamical scenario whose associated
stationary probability density function is exactly a previously proposed one to
adjust high-frequency traded volume distributions. This dynamical conjecture,
physically connected to superstatiscs, which is intimately related with the
current nonextensive statistical mechanics framework, is based on the idea of
local fluctuations in the mean traded volume associated to financial markets
agents herding behaviour. The corroboration of this mesoscopic model is done by
modelising NASDAQ 1 and 2 minute stock market traded volume
Strengths, innovation, and opportunities in a burgeoning industry: an exploratory study
Purpose: The purpose of this paper is to examine key areas related to the craft brewing industry from the perspective of operators of micro and small craft breweries, and propose a framework based on the resourced-based theory of the firm and the theory of innovation. The areas investigated include participants’ perceived strengths of their craft brewery, involvement in innovative practices, opportunities for the craft brewing firm, and potential differences related to these areas based on the demographic characteristics of participants and their breweries. Design/methodology/approach: Given its growing significance and economic contribution, the US craft brewery industry was chosen for this study. An online questionnaire was designed to gather data from craft brewery operators across the nation. Findings: Product and service quality, knowledge, reputation, and expertise were revealed as key strengths, while creating new recipes and using social media tools were the most considered ways of innovating. Furthermore, opportunities were perceived through craft beer tourism, increased consumption, and quality improvements. Statistically significant differences emerged, particularly based on production levels, staff numbers, and involvement/no involvement in exports. Various associations between the findings and the adopted theoretical frameworks were revealed. Originality/value: In terms of originality, the proposed refinement based on the adopted theoretical frameworks and findings facilitates understanding of the significance of resources and innovation, particularly for firms operating in a growing industry. Regarding value, the findings have important implications for the industry, for instance, in the marketing of craft brewing, as well as in the development of new craft brewing products. © 2018, Emerald Publishing Limited
Micro enterprises, self-efficacy and knowledge acquisition: evidence from Greece and Spain
Purpose: The purpose of this exploratory study is to investigate the significance of self-efficacy and knowledge acquisition among micro businesses operating in challenging economic environments. The study uses social cognitive theory (SCT) and the knowledge-based theory of the firm (KBTF), and it proposes a refinement of these theoretical frameworks in the context of the study. Design/methodology/approach: A case method was chosen, and face-to-face interviews with 14 owners of firms in island and rural regions of Greece and Spain were conducted. Findings: Content analysis identified the importance of self-efficacy, primarily illustrated by entrepreneurs’ determination and self-motivation, propensity to take risks and ability to anticipate consequences of their actions. Acquisition and accumulation of explicit knowledge, particularly through generational or mentoring processes, and subsequent wealth of tacit knowledge, also emerged as very significant in preparing and guiding entrepreneurs. Various links between the adopted theories and findings emerged, particularly regarding forethought, vicarious learning (SCT) and specialisation in knowledge acquisition (KBTF). Originality/value: The proposed theoretical refinement based on the SCT and KBTF paradigms allows for a more rigorous, in-depth reflection on the links between cognitive elements present in the participating micro entrepreneurs and knowledge-based attributes on their ability to increase organisational resilience. The study also contributes toward the micro business literature and addresses a knowledge gap, particularly, in that contemporary research has not explored entrepreneurial motivations among small firm entrepreneurs. Finally, the practical implications emerging from the findings provide a platform for various stakeholders (associations, government agencies) to appreciate and support entrepreneurs’ needs, notably, of acquiring, increasing and sharing knowledge. © 2018, Emerald Publishing Limited
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