2,724 research outputs found
On the relationship between pump chirp and single-photon chirp in spontaneous parametric downconversion
We study the chronocyclic character, i.e. the joint temporal and spectral
properties, of the single-photon constituents of photon pairs generated by
spontaneous parametric down conversion. In particular we study how single
photon properties, including purity and single-photon chirp, depend on photon
pair properties, including the type of signal-idler spectral and correlations
and the level of pump chirp.Comment: 13 pages, 6 figure
Electrical manipulation of spin states in a single electrostatically gated transition-metal complex
We demonstrate an electrically controlled high-spin (S=5/2) to low-spin
(S=1/2) transition in a three-terminal device incorporating a single Mn2+ ion
coordinated by two terpyridine ligands. By adjusting the gate-voltage we reduce
the terpyridine moiety and thereby strengthen the ligand-field on the Mn-atom.
Adding a single electron thus stabilizes the low-spin configuration and the
corresponding sequential tunnelling current is suppressed by spin-blockade.
From low-temperature inelastic cotunneling spectroscopy, we infer the
magnetic excitation spectrum of the molecule and uncover also a strongly
gate-dependent singlet-triplet splitting on the low-spin side. The measured
bias-spectroscopy is shown to be consistent with an exact diagonalization of
the Mn-complex, and an interpretation of the data is given in terms of a
simplified effective model.Comment: Will appear soon in Nanoletter
Predicted Colors and Flux Densities of Protostars in the Herschel PACS and SPIRE Filters
Upcoming surveys with the Herschel Space Observatory will yield far-IR
photometry of large samples of young stellar objects, which will require
careful interpretation. We investigate the color and luminosity diagnostics
based on Herschel broad-band filters to identify and discern the properties of
low-mass protostars. We compute a grid of 2,016 protostars in various physical
congurations, present the expected flux densities and flux density ratios for
this grid of protostars, and compare Herschel observations of three protostars
to the model results. These provide useful constraints on the range of colors
and fluxes of protostar in the Herschel filters. We find that Herschel data
alone is likely a useful diagnostic of the envelope properties of young starsComment: Part of HOPS KP papers to the Herschel special A&A issu
Engineering integrated pure narrow-band photon sources
Engineering and controlling well defined states of light for quantum
information applications is of increasing importance as the complexity of
quantum systems grows. For example, in quantum networks high multi-photon
interference visibility requires properly devised single mode sources. In this
paper we propose a spontaneous parametric down conversion source based on an
integrated cavity-waveguide, where single narrow-band, possibly distinct,
spectral modes for the idler and the signal fields can be generated. This mode
selection takes advantage of the clustering effect, due to the intrinsic
dispersion of the nonlinear material. In combination with a CW laser and fast
detection, our approach provides a means to engineer a source that can
efficiently generate pure photons, without filtering, that is compatible with
long distance quantum communication. Furthermore, it is extremely flexible and
could easily be adapted to a wide variety of wavelengths and applications.Comment: 13 pages, 7 figure
Statistical mixing and aggregation in Feller diffusion
We consider Feller mean-reverting square-root diffusion, which has been
applied to model a wide variety of processes with linearly state-dependent
diffusion, such as stochastic volatility and interest rates in finance, and
neuronal and populations dynamics in natural sciences. We focus on the
statistical mixing (or superstatistical) process in which the parameter related
to the mean value can fluctuate - a plausible mechanism for the emergence of
heavy-tailed distributions. We obtain analytical results for the associated
probability density function (both stationary and time dependent), its
correlation structure and aggregation properties. Our results are applied to
explain the statistics of stock traded volume at different aggregation scales.Comment: 16 pages, 3 figures. To be published in Journal of Statistical
Mechanics: Theory and Experimen
Vibrational Excitations in Weakly Coupled Single-Molecule Junctions: A Computational Analysis
In bulk systems, molecules are routinely identified by their vibrational
spectrum using Raman or infrared spectroscopy. In recent years, vibrational
excitation lines have been observed in low-temperature conductance measurements
on single molecule junctions and they can provide a similar means of
identification. We present a method to efficiently calculate these excitation
lines in weakly coupled, gateable single-molecule junctions, using a
combination of ab initio density functional theory and rate equations. Our
method takes transitions from excited to excited vibrational state into account
by evaluating the Franck-Condon factors for an arbitrary number of vibrational
quanta, and is therefore able to predict qualitatively different behaviour from
calculations limited to transitions from ground state to excited vibrational
state. We find that the vibrational spectrum is sensitive to the molecular
contact geometry and the charge state, and that it is generally necessary to
take more than one vibrational quantum into account. Quantitative comparison to
previously reported measurements on pi-conjugated molecules reveals that our
method is able to characterize the vibrational excitations and can be used to
identify single molecules in a junction. The method is computationally feasible
on commodity hardware.Comment: 9 pages, 7 figure
Switchable Coupling of Vibrations to Two-Electron Carbon-Nanotube Quantum Dot States
We report transport measurements on a quantum dot in a partly suspended
carbon nanotube. Electrostatic tuning allows us to modify and even switch 'on'
and 'off' the coupling to the quantized stretching vibration across several
charge states. The magnetic-field dependence indicates that only the
two-electron spin-triplet excited state couples to the mechanical motion,
indicating mechanical coupling to both the valley degree of freedom and the
exchange interaction, in contrast to standard models
Hier ist wahrhaftig ein Loch im Himmel - The NGC 1999 dark globule is not a globule
The NGC 1999 reflection nebula features a dark patch with a size of ~10,000
AU, which has been interpreted as a small, dense foreground globule and
possible site of imminent star formation. We present Herschel PACS far-infrared
70 and 160mum maps, which reveal a flux deficit at the location of the globule.
We estimate the globule mass needed to produce such an absorption feature to be
a few tenths to a few Msun. Inspired by this Herschel observation, we obtained
APEX LABOCA and SABOCA submillimeter continuum maps, and Magellan PANIC
near-infrared images of the region. We do not detect a submillimer source at
the location of the Herschel flux decrement; furthermore our observations place
an upper limit on the mass of the globule of ~2.4x10^-2 Msun. Indeed, the
submillimeter maps appear to show a flux depression as well. Furthermore, the
near-infrared images detect faint background stars that are less affected by
extinction inside the dark patch than in its surroundings. We suggest that the
dark patch is in fact a hole or cavity in the material producing the NGC 1999
reflection nebula, excavated by protostellar jets from the V 380 Ori multiple
system.Comment: accepted for the A&A Herschel issue; 7 page
Evaluation of a candidate breast cancer associated SNP in ERCC4 as a risk modifier in BRCA1 and BRCA2 mutation carriers. Results from the Consortium of Investigators of Modifiers of BRCA1/BRCA2 (CIMBA)
Background: In this study we aimed to evaluate the role of a SNP in intron 1 of the ERCC4 gene (rs744154), previously reported to be associated with a reduced risk of breast cancer in the general population, as a breast cancer risk modifier in BRCA1 and BRCA2 mutation carriers. Methods: We have genotyped rs744154 in 9408 BRCA1 and 5632 BRCA2 mutation carriers from the Consortium of Investigators of Modifiers of BRCA1/2 (CIMBA) and assessed its association with breast cancer risk using a retrospective weighted cohort approach. Results: We found no evidence of association with breast cancer risk for BRCA1 (per-allele HR: 0.98, 95% CI: 0.93–1.04, P=0.5) or BRCA2 (per-allele HR: 0.97, 95% CI: 0.89–1.06, P=0.5) mutation carriers. Conclusion: This SNP is not a significant modifier of breast cancer risk for mutation carriers, though weak associations cannot be ruled out. A Osorio1, R L Milne2, G Pita3, P Peterlongo4,5, T Heikkinen6, J Simard7, G Chenevix-Trench8, A B Spurdle8, J Beesley8, X Chen8, S Healey8, KConFab9, S L Neuhausen10, Y C Ding10, F J Couch11,12, X Wang11, N Lindor13, S Manoukian4, M Barile14, A Viel15, L Tizzoni5,16, C I Szabo17, L Foretova18, M Zikan19, K Claes20, M H Greene21, P Mai21, G Rennert22, F Lejbkowicz22, O Barnett-Griness22, I L Andrulis23,24, H Ozcelik24, N Weerasooriya23, OCGN23, A-M Gerdes25, M Thomassen25, D G Cruger26, M A Caligo27, E Friedman28,29, B Kaufman28,29, Y Laitman28, S Cohen28, T Kontorovich28, R Gershoni-Baruch30, E Dagan31,32, H Jernström33, M S Askmalm34, B Arver35, B Malmer36, SWE-BRCA37, S M Domchek38, K L Nathanson38, J Brunet39, T RamĂłn y Cajal40, D Yannoukakos41, U Hamann42, HEBON37, F B L Hogervorst43, S Verhoef43, EB GĂłmez GarcĂa44,45, J T Wijnen46,47, A van den Ouweland48, EMBRACE37, D F Easton49, S Peock49, M Cook49, C T Oliver49, D Frost49, C Luccarini50, D G Evans51, F Lalloo51, R Eeles52, G Pichert53, J Cook54, S Hodgson55, P J Morrison56, F Douglas57, A K Godwin58, GEMO59,60,61, O M Sinilnikova59,60, L Barjhoux59,60, D Stoppa-Lyonnet61, V Moncoutier61, S Giraud59, C Cassini62,63, L Olivier-Faivre62,63, F RĂ©villion64, J-P Peyrat64, D Muller65, J-P Fricker65, H T Lynch66, E M John67, S Buys68, M Daly69, J L Hopper70, M B Terry71, A Miron72, Y Yassin72, D Goldgar73, Breast Cancer Family Registry37, C F Singer74, D Gschwantler-Kaulich74, G Pfeiler74, A-C Spiess74, Thomas v O Hansen75, O T Johannsson76, T Kirchhoff77, K Offit77, K Kosarin77, M Piedmonte78, G C Rodriguez79, K Wakeley80, J F Boggess81, J Basil82, P E Schwartz83, S V Blank84, A E Toland85, M Montagna86, C Casella87, E N Imyanitov88, A Allavena89, R K Schmutzler90, B Versmold90, C Engel91, A Meindl92, N Ditsch93, N Arnold94, D Niederacher95, H DeiĂźler96, B Fiebig97, R Varon-Mateeva98, D Schaefer99, U G Froster100, T Caldes101, M de la Hoya101, L McGuffog49, A C Antoniou49, H Nevanlinna6, P Radice4,5 and J BenĂtez1,3 on behalf of CIMB
Electronic and optical properties of lead iodide
ABSTRACT: Lead iodide (PbI2) is a very important material with a technological applicability as a room-temperature radiation detector. It is a wide-band-gap semiconductor (Eg.2 eV) with high environmental stability efficiency. The performance of the detector cannot be fully understood unless its electronic and optical properties are determined. Recently, its band-gap energy and thermal properties were determined by photoacoustic spectroscopy. A single crystal of PbI2 was grown by the Bridgman method with the c-axis oriented perpendicular to the growth axis. The purpose of this work is to obtain the electronic structure of PbI2, its dielectric functions e 1 and e 2 by ellipsometry and theoretically by full-potential linear muffin-tinorbital ~FPLMTO! method, and the temperature dependence of the measured band-gap energy by optica absorption. The obtained Eg(T) can be fitted by two different methods, leading to Eg ~0 K! and Eg ~300 K!
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