725 research outputs found
Integrated waveguides and deterministically positioned nitrogen vacancy centers in diamond created by femtosecond laser writing
Diamond's nitrogen vacancy (NV) center is an optically active defect with
long spin coherence times, showing great potential for both efficient nanoscale
magnetometry and quantum information processing schemes. Recently, both the
formation of buried 3D optical waveguides and high quality single NVs in
diamond were demonstrated using the versatile femtosecond laser-writing
technique. However, until now, combining these technologies has been an
outstanding challenge. In this work, we fabricate laser written photonic
waveguides in quantum grade diamond which are aligned to within micron
resolution to single laser-written NVs, enabling an integrated platform
providing deterministically positioned waveguide-coupled NVs. This fabrication
technology opens the way towards on-chip optical routing of single photons
between NVs and optically integrated spin-based sensing
Velocity Map Imaging the Scattering Plane of Gas Surface Collisions
The ability of gas-surface dynamics studies to resolve the velocity
distribution of the scattered species in the 2D sacattering plane has been
limited by technical capabilities and only a few different approaches have been
explored in recent years. In comparison, gas-phase scattering studies have been
transformed by the near ubiquitous use of velocity map imaging. We describe an
innovative means of introducing a surface within the electric field of a
typical velocity map imaging experiment. The retention of optimum velocity
mapping conditions was demonstrated by measurements of iodomethane-d3
photodissociation and SIMION calculations. To demonstrate the systems
capabilities the velocity distributions of ammonia molecules scattered from a
PTFE surface have been measured for multiple product rotational states.Comment: 8 pages, 5 figures, to be submitted to journa
Transit Timing and Duration Variations for the Discovery and Characterization of Exoplanets
Transiting exoplanets in multi-planet systems have non-Keplerian orbits which
can cause the times and durations of transits to vary. The theory and
observations of transit timing variations (TTV) and transit duration variations
(TDV) are reviewed. Since the last review, the Kepler spacecraft has detected
several hundred perturbed planets. In a few cases, these data have been used to
discover additional planets, similar to the historical discovery of Neptune in
our own Solar System. However, the more impactful aspect of TTV and TDV studies
has been characterization of planetary systems in which multiple planets
transit. After addressing the equations of motion and parameter scalings, the
main dynamical mechanisms for TTV and TDV are described, with citations to the
observational literature for real examples. We describe parameter constraints,
particularly the origin of the mass/eccentricity degeneracy and how it is
overcome by the high-frequency component of the signal. On the observational
side, derivation of timing precision and introduction to the timing diagram are
given. Science results are reviewed, with an emphasis on mass measurements of
transiting sub-Neptunes and super-Earths, from which bulk compositions may be
inferred.Comment: Revised version. Invited review submitted to 'Handbook of
Exoplanets,' Exoplanet Discovery Methods section, Springer Reference Works,
Juan Antonio Belmonte and Hans Deeg, Eds. TeX and figures may be found at
https://github.com/ericagol/TTV_revie
Underground railroads: citizen entitlements and unauthorized mobility in the antebellum period and today
In recent years, some scholars and prominent political figures have advocated the deepening of North American integration on roughly the European Union model, including the creation of new political institutions and the free movement of workers across borders. The construction of such a North American Union, if it included even a very thin trans-state citizenship regime, could represent the most significant expansion of individual entitlements in the region since citizenship was extended to former slaves in the United States. With such a possibility as its starting point, this article explores some striking parallels between the mass, legally prohibited movement across boundaries by fugitive slaves in the pre-Civil War period, and that by current unauthorized migrants to the United States. Both were, or are, met on their journeys by historically parallel groups of would-be helpers and hinderers. Their unauthorized movements in both periods serve as important signals of incomplete entitlements or institutional protections. Most crucially, moral arguments for extending fuller entitlements to both groups are shown here to be less distinct than may be prima facie evident, reinforcing the case for expanding and deepening the regional membership regime
Coherent, mechanical control of a single electronic spin
The ability to control and manipulate spins via electrical, magnetic and
optical means has generated numerous applications in metrology and quantum
information science in recent years. A promising alternative method for spin
manipulation is the use of mechanical motion, where the oscillation of a
mechanical resonator can be magnetically coupled to a spins magnetic dipole,
which could enable scalable quantum information architectures9 and sensitive
nanoscale magnetometry. To date, however, only population control of spins has
been realized via classical motion of a mechanical resonator. Here, we
demonstrate coherent mechanical control of an individual spin under ambient
conditions using the driven motion of a mechanical resonator that is
magnetically coupled to the electronic spin of a single nitrogen-vacancy (NV)
color center in diamond. Coherent control of this hybrid mechanical/spin system
is achieved by synchronizing pulsed spin-addressing protocols (involving
optical and radiofrequency fields) to the motion of the driven oscillator,
which allows coherent mechanical manipulation of both the population and phase
of the spin via motion-induced Zeeman shifts of the NV spins energy. We
demonstrate applications of this coherent mechanical spin-control technique to
sensitive nanoscale scanning magnetometry.Comment: 6 pages, 4 figure
Highly controlled, reproducible measurements of aerosol emissions from combustion of a common African biofuel source
Particulate emissions from biomass burning can both alter the atmosphere's radiative
balance and cause significant harm to human health. However, due to the large
effect on emissions caused by even small alterations to the way in which
a fuel burns, it is difficult to study particulate production of biomass
combustion mechanistically and in a repeatable manner. In order to address
this gap, in this study, small wood samples sourced from Côte D'Ivoire in
West Africa were burned in a highly controlled laboratory environment. The
shape and mass of samples, available airflow and surrounding thermal
environment were carefully regulated. Organic aerosol and refractory black
carbon emissions were measured in real time using an Aerosol Mass
Spectrometer and a Single Particle Soot Photometer, respectively. This
methodology produced remarkably repeatable results, allowing aerosol
emissions to be mapped directly onto different phases of combustion.
Emissions from pyrolysis were visible as a distinct phase before flaming was
established. After flaming combustion was initiated, a black-carbon-dominant
flame was observed during which very little organic aerosol was produced,
followed by a period that was dominated by organic-carbon-producing
smouldering combustion, despite the presence of residual flaming. During
pyrolysis and smouldering, the two phases producing organic aerosol, distinct
mass spectral signatures that correspond to previously reported variations in
biofuel emissions measured in the atmosphere are found. Organic aerosol
emission factors averaged over an entire combustion event were found to be
representative of the time spent in the pyrolysis and smouldering phases,
rather than reflecting a coupling between emissions and the mass loss of the
sample. Further exploration of aerosol yields from similarly carefully
controlled fires and a careful comparison with data from macroscopic fires
and real-world emissions will help to deliver greater constraints on the
variability of particulate emissions in atmospheric systems
A Multipronged Comparative Study of the Ultraviolet Photochemistry of 2-, 3-, and 4-Chlorophenol in the Gas Phase
The S1(1ππ*) state of the (dominant) syn-conformer of 2-chlorophenol (2-ClPhOH) in the gas phase has a subpicosecond lifetime, whereas the corresponding S1 states of 3- and 4-ClPhOH have lifetimes that are, respectively, ∼2 and ∼3-orders of magnitude longer. A range of experimental techniques–electronic spectroscopy, ultrafast time-resolved photoion and photoelectron spectroscopies, H Rydberg atom photofragment translational spectroscopy, velocity map imaging, and time-resolved Fourier transform infrared emission spectroscopy–as well as electronic structure calculations (of key regions of the multidimensional ground (S0) state potential energy surface (PES) and selected cuts through the first few excited singlet PESs) have been used in the quest to explain these striking differences in excited state lifetime. The intramolecular O–H···Cl hydrogen bond specific to syn-2-ClPhOH is key. It encourages partial charge transfer and preferential stabilization of the diabatic 1πσ* potential (relative to that of the 1ππ* state) upon stretching the C–Cl bond, with the result that initial C–Cl bond extension on the adiabatic S1 PES offers an essentially barrierless internal conversion pathway via regions of conical intersection with the S0 PES. Intramolecular hydrogen bonding is thus seen to facilitate the type of heterolytic dissociation more typically encountered in solution studies
Bile acid: a potential inducer of colon cancer stem cells
Background: Although the unconjugated secondary bile acids, specifically deoxycholic acid (DCA) and lithocholic acid (LCA), are considered to be risk factors for colorectal cancer, the precise mechanism(s) by which they regulate carcinogenesis is poorly understood. We hypothesize that the cytotoxic bile acids may promote stemness in colonic epithelial cells leading to generation of cancer stem cells (CSCs) that play a role in the development and progression of colon cancer. Methods: Normal human colonic epithelial cells (HCoEpiC) were used to study bile acid DCA/LCA-mediated induction of CSCs. The expression of CSC markers was measured by real-time qPCR. Flow cytometry was used to isolate CSCs. T-cell factor/lymphoid-enhancing factor (TCF/LEF) luciferase assay was employed to examine the transcriptional activity of β-catenin. Downregulation of muscarinic 3 receptor (M3R) was achieved through transfection of corresponding siRNA. Results: We found DCA/LCA to induce CSCs in normal human colonic epithelial cells, as evidenced by the increased proportion of CSCs, elevated levels of several CSC markers, as well as a number of epithelial– mesenchymal transition markers together with increased colonosphere formation, drug exclusion, ABCB1 and ABCG2 expression, and induction of M3R, p-EGFR, matrix metallopeptidases, and c-Myc. Inhibition of M3R signaling greatly suppressed DCA/LCA induction of the CSC marker ALDHA1 and also c-Myc mRNA expression as well as transcriptional activation of TCF/LEF. Conclusions: Our results suggest that bile acids, specifically DCA and LCA, induce cancer stemness in colonic epithelial cells by modulating M3R and Wnt/β-catenin signaling and thus could be considered promoters of colon cancer
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