7,324 research outputs found
Phase space polarization and the topological string: a case study
We review and elaborate on our discussion in hep-th/0606112 on the interplay
between the target space and the worldsheet description of the open topological
string partition function, for the example of the conifold. We discuss the
appropriate phase space and canonical form for the system. We find a map
between choices of polarization and the worldsheet description, based on which
we study the behavior of the partition function under canonical
transformations.Comment: 18 pages, invited review for MPL
Persistent currents in carbon nanotubes
Persistent currents driven by a static magnetic flux parallel to the carbon
nanotube axis are investigated. Owing to the hexagonal symmetry of graphene the
Fermi contour expected for a 2D-lattice reduces to two points. However the
electron or hole doping shifts the Fermi energy upwards or downwards and as a
result, the shape of the Fermi surface changes. Such a hole doping leading to
the Fermi level shift of (more or less) 1eV has been recently observed
experimentally. In this paper we show that the shift of the Fermi energy
changes dramatically the persistent currents and discuss the electronic
structure and possible currents for zigzag as well as armchair nanotubes.Comment: 8 text pages, 6 figures, to appear in Physics Letters
Very low shot noise in carbon nanotubes
We have performed noise measurements on suspended ropes of single wall carbon
nanotubes (SWNT) between 1 and 300 K for different values of dc current through
the ropes. We find that the shot noise is suppressed by more than a factor 100
compared to the full shot noise 2eI. We have also measured an individual SWNT
and found a level of noise which is smaller than the minimum expected. Another
finding is the very low level of 1/f noise, which is significantly lower than
previous observations. We propose two possible interpretations for this strong
shot noise reduction: i) Transport within a rope takes place through a few
nearly ballistic tubes within a rope and possibly involves non integer
effective charges. ii) A substantial fraction of the tubes conduct with a
strong reduction of effective charge (by more than a factor 50).Comment: Submitted to Eur. Phys. J. B (Jan. 2002) Higher resolution pictures
are posted on http://www.lps.u-psud.fr/Collectif/gr_07/publications.htm
New Cepheid variables in the young open clusters Berkeley 51 and Berkeley 55
As part of a wider investigation of evolved massive stars in Galactic open clusters, we have spectroscopically identified three candidate classical Cepheids in the little-studied clusters Berkeley 51, Berkeley 55 and NGC 6603. Using new multi-epoch photometry, we confirm that Be 51 #162 and Be 55 #107 are bona fide Cepheids, with pulsation periods of 9.83±0.01 d and 5.850±0.005 d respectively, while NGC 6603 star W2249 does not show significant photometric variability. Using the period-luminosity relationship for Cepheid variables, we determine a distance to Be 51 of 5.3 +1.0 −0.8 kpc and an age of 44 +9 −8 Myr, placing it in a sparsely-attested region of the Perseus arm. For Be 55, we find a distance of 2.2±0.3 kpc and age of 63 +12 −11 Myr, locating the cluster in the Local arm. Taken together with our recent discovery of a long-period Cepheid in the starburst cluster VdBH222, these represent an important increase in the number of young, massive Cepheids known in Galactic open clusters. We also consider new Gaia (data release 2) parallaxes and proper motions for members of Be 51 and Be 55; the uncertainties on the parallaxes do not allow us to refine our distance estimates to these clusters, but the well-constrained proper motion measurements furnish further confirmation of cluster membership. However, future final Gaia parallaxes for such objects should provide valuable independent distance measurements, improving the calibration of the period-luminosity relationship, with implications for the distance ladder out to cosmological scales
Compiling Linguistic Constraints into Finite State Automata
International audienceThis paper deals with linguistic constraints encoded in the form of (binary) tables, generally called lexicon-grammar tables. We describe a unified method to compile sets of tables of linguistic constraints into Finite State Automata. This method has been practically implemented in the linguistic platform Unitex
Distribution of dust clouds around the central engine of NGC 1068
We studied the distribution of dust clouds around the central engine of NGC
1068 based on shifted-and-added 8.8 - 12.3 micron (MIR) multi-filter images and
3.0 - 3.9 micron (L-band) spectra obtained with the Subaru Telescope. In a
region of 100 pc (1.4") around the central peak, we successfully constructed
maps of color temperatures and emissivities of the MIR and L-band continua as
well as the 9.7 micron and 3.4 micron dust features with spatial resolutions of
26 pc (0.37") in the MIR and 22 pc (0.3") in the L-band. Our main results are:
1) color temperature of the MIR continuum scatters around the thermal
equilibrium temperature with the central engine as the heat source while that
of the L-band continuum is higher and independent upon distance from the
central engine; 2) the peak of the 9.7 micron silicate absorption feature is
shifted to a longer wavelength at some locations; 3) the ratio of the optical
depths of the dust features is different from the Galactic values and show
complicated spatial distribution; and 4) there is a pie shaped warm dust cloud
as an enhancement in the emissivity of the MIR continuum extending about 50 pc
to the north from the central engine. We speculate that material falls into the
central engine through this cloud.Comment: 26 pages, 9 figures. Accepted for publication on Ap
High Resolution Imaging of the Magnetic Field in the central parsec of the Galaxy
We discuss a high resolution (FWHM~ 0.45 arcsec) image of the emissive
polarization from warm dust in the minispiral in the Galactic Centre and
discuss the implications for the magnetic field in the dusty filaments. The
image was obtained at a wavelength of 12.5 microns with the CanariCam multimode
mid-infrared imager on the Gran Telescopio Canarias. It confirms the results
obtained from previous observations but also reveals new details of the
polarization structures. In particular, we identify regions of coherent
magnetic field emission at position angles of ~45 deg to the predominantly
north--south run of field lines in the Northern Arm which may be related to
orbital motions inclined to the general flow of the Northern Arm. The luminous
stars that have been identified as bow-shock sources in the Northern Arm do not
disrupt or dilute the field but are linked by a coherent field structure,
implying that the winds from these objects may push and compress the field but
do not overwhelm it. The magnetic field in the the low surface brightness
regions in the East-West Bar to the south of SgrA* lies along the Bar, but the
brighter regions generally have different polarization position angles,
suggesting that they are distinct structures. In the region of the Northern Arm
sampled here, there is only a weak correlation between the intensity of the
emission and the degree of polarization. This is consistent with saturated
grain alignment where the degree of polarization depends on geometric effects,
including the angle of inclination of the field to the line of sight and
superposition of filaments with different field directions, rather than the
alignment efficiency.Comment: 9 pages, 3 figures, Proceedings of Cosmic Dust X, held in Mitaka,
Japan in August 201
Tuning laser-induced bandgaps in graphene
Could a laser field lead to the much sought-after tunable bandgaps in
graphene? By using Floquet theory combined with Green's functions techniques,
we predict that a laser field in the mid-infrared range can produce observable
bandgaps in the electronic structure of graphene. Furthermore, we show how they
can be tuned by using the laser polarization. Our results could serve as a
guidance to design opto-electronic nano-devices.Comment: 4 pages, 3 figures, to appear in Applied Physics Letter
Factors in the practice environment of nurses working in inpatient mental health: A partial least squares path modeling approach
Background: Developing a therapeutic relationship with consumers is considered as the central aspect of nursing work in mental health. The importance of this relationship stems from its association with enhanced patient care and improved patient outcomes. Factors within the practice environment may influence the nurse's ability to engage effectively in this relationship. Objective: This study explored a model that added characteristics of the individual and practice environment to a central framework incorporating therapeutic commitment: a nurse's ability and willingness to engage in a therapeutic relationship. Setting and participants: Data were collected at six mental health nursing units in five public general acute hospitals in New South Wales, Australia for 14 days per unit, between 2005 and 2006. All nurses in participating wards were invited to partake in the study. Seventy-six (51%) responses were analyzed. Method: The data were collected using a Nurse Survey inclusive of the Practice Environment Scale of the Nursing Work Index (NWI-PES), and the Mental Health Problems Perception Questionnaire (MHPPQ). A Unit Profile form was used concurrently to collect staffing, skill mix and patient turnover data. Partial least squares path modeling (PLS-PM) was chosen as the analytical method to test the model and identify the most influential factors. Results: Experienced nurses who perceived themselves to be competent and supported were more likely to express a willingness to engage therapeutically with patients. Environmental factors associated with these perceptions included foundations of quality nursing care, opportunities to participate in hospital affairs and clinical supervision. Not all elements in the proposed model were supported. Conclusion: Positive hospital practice environments can improve the capacity of nurses working in mental health to engage therapeutically with patients. Specific approaches may include access to preceptorship, continued education and career development opportunities, together with clinical supervision, improved continuity of care, and the involvement of mental health nurses in the governance of the hospital. © 2011 Elsevier Ltd
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