114 research outputs found
Enhanced Two-Photon Absorption in a Hollow-Core Photonic Bandgap Fiber
We show that two-photon absorption (TPA) in Rubidium atoms can be greatly
enhanced by the use of a hollow-core photonic bandgap fiber. We investigate
off-resonant, degenerate Doppler-free TPA on the 5S1/2 - 5D5/2 transition and
observe 1% absorption of a pump beam with a total power of only 1 mW in the
fiber. These results are verified by measuring the amount of emitted blue
fluorescence and are consistent with the theoretical predictions which indicate
that transit time effects play an important role in determining the two-photon
absorption cross-section in a confined geometry.Comment: 5 pages, 6 figure
Zeeman Relaxation of Cold Atomic Iron and Nickel in Collisions with 3He
We have measured the ratio of the diffusion cross-section to the angular
momentum reorientation cross-section in the colliding Fe-3He and Ni-3He
systems. Nickel (Ni) and iron (Fe) atoms are introduced via laser ablation into
a cryogenically cooled experimental cell containing cold (< 1 K) 3He buffer
gas. Elastic collisions rapidly cool the translational temperature of the
ablated atoms to the helium temperature. The cross-section ratio is extracted
by measuring the decays of the atomic Zeeman sublevels. For our experimental
conditions, thermal energy is comparable to the Zeeman splitting. As a result,
thermal excitations between Zeeman sublevels significantly impact the observed
decay. To determine the cross-section ratio accurately, we introduce a model of
Zeeman state dynamics that includes thermal excitations. We find the
cross-section ratio for Ni-3He = 5 x 10^3 and Fe-3He <= 3 x 10^3 at 0.75 K in a
0.8 T magnetic field. These measurements are interpreted in the context of
submerged shell suppression of spin relaxation as studied previously in
transition metals and rare earth atoms.Comment: 10 pages, 5 figures; submitted to Phys. Rev.
Optical pumping via incoherent Raman transitions
A new optical pumping scheme is presented that uses incoherent Raman
transitions to prepare a trapped Cesium atom in a specific Zeeman state within
the 6S_{1/2}, F=3 hyperfine manifold. An important advantage of this scheme
over existing optical pumping schemes is that the atom can be prepared in any
of the F=3 Zeeman states. We demonstrate the scheme in the context of cavity
quantum electrodynamics, but the technique is equally applicable to a wide
variety of atomic systems with hyperfine ground-state structure.Comment: 8 pages, 4 figure
Differential expression of DHHC9 in microsatellite stable and instable human colorectal cancer subgroups
Microarray analysis on pooled samples has previously identified ZDHHC9 (DHHC9) to be upregulated in colon adenocarcinoma compared to normal colon mucosa. Analyses of 168 samples from proximal and distal adenocarcinomas using U133plus2.0 microarrays validated these findings, showing a significant two-fold (log 2) upregulation of DHHC9 transcript (P<10(−6)). The upregulation was more striking in microsatellite stable (MSS), than in microsatellite instable (MSI), tumours. Genes known to interact with DHHC9 as H-Ras or N-Ras did not show expression differences between MSS and MSI. Immunohistochemical analysis was performed on 60 colon adenocarcinomas, previously analysed on microarrays, as well as on tissue microarrays with 40 stage I–IV tumours and 46 tumours from different organ sites. DHHC9 protein was strongly expressed in MSS compared to MSI tumours, readily detectable in premalignant lesions, compared to the rare expression seen in normal mucosa. DHHC9 was specific for tumours of the gastrointestinal tract and localised to the Golgi apparatus, in vitro and in vivo. Overexpression of DHHC9 decreased the proliferation of SW480 and CaCo2 MSS cell lines significantly. In conclusion, DHHC9 is a gastrointestinal-related protein highly expressed in MSS colon tumours. The palmitoyl transferase activity, modifying N-Ras and H-Ras, suggests DHHC9 as a target for anticancer drug design
Coherent Dual Comb Spectroscopy at High Signal to Noise
Two frequency combs can be used to measure the full complex response of a
sample in a configuration which can be alternatively viewed as the equivalent
of a dispersive Fourier transform spectrometer, infrared time domain
spectrometer, or a multiheterodyne laser spectrometer. This dual comb
spectrometer retains the frequency accuracy and resolution inherent to the comb
sources. We discuss, in detail, the specific design of our coherent dual-comb
spectrometer and demonstrate the potential of this technique by measuring the
first overtone vibration of hydrogen cyanide, centered at 194 THz (1545 nm). We
measure the fully normalized, complex response of the gas over a 9 THz
bandwidth at 220 MHz frequency resolution yielding 41,000 resolution elements.
The average spectral signal-to-noise ratio (SNR) is 2,500 for both the
fractional absorption and the phase, with a peak SNR of 4,000 corresponding to
a fractional absorption sensitivity of 0.025% and phase sensitivity of 250
microradians. As the spectral coverage of combs expands, this dual-comb
spectroscopy could provide high frequency accuracy and resolution measurements
of a complex sample response across a range of spectral regions.Comment: 18 pages, 8 figures updated references, updated to match publication
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Sub-Doppler spectroscopy of Rb atoms in a sub-micron vapor cell in the presence of a magnetic field
We report the first use of an extremely thin vapor cell (thickness ~ 400 nm)
to study the magnetic-field dependence of laser-induced-fluorescence excitation
spectra of alkali atoms. This thin cell allows for sub-Doppler resolution
without the complexity of atomic beam or laser cooling techniques. This
technique is used to study the laser-induced-fluorescence excitation spectra of
Rb in a 50 G magnetic field. At this field strength the electronic angular
momentum J and nuclear angular momentum I are only partially decoupled. As a
result of the mixing of wavefunctions of different hyperfine states, we observe
a nonlinear Zeeman effect for each sublevel, a substantial modification of the
transition probabilities between different magnetic sublevels, and the
appearance of transitions that are strictly forbidden in the absence of the
magnetic field. For the case of right- and left- handed circularly polarized
laser excitation, the fluorescence spectra differs qualitatively. Well
pronounced magnetic field induced circular dichroism is observed. These
observations are explained with a standard approach that describes the partial
decoupling of I and J states
Tumour invasiveness, the local and systemic environment and the basis of staging systems in colorectal cancer
background: The present study aimed to examine the relationship between tumour invasiveness (T stage), the local and systemic environment and cancer-specific survival (CSS) of patients with primary operable colorectal cancer.
methods: The tumour microenvironment was examined using measures of the inflammatory infiltrate (Klintrup-Makinen (KM) grade and Immunoscore), tumour stroma percentage (TSP) and tumour budding. The systemic inflammatory environment was examined using modified Glasgow Prognostic Score (mGPS) and neutrophil:lymphocyte ratio (NLR). A 5-year CSS was examined.
results: A total of 331 patients were included. Increasing T stage was associated with colonic primary, N stage, poor differentiation, margin involvement and venous invasion (P<0.05). T stage was significantly associated with KM grade (P=0.001), Immunoscore (P=0.016), TSP (P=0.006), tumour budding (P<0.001), and elevated mGPS and NLR (both P<0.05). In patients with T3 cancer, N stage stratified survival from 88 to 64%, whereas Immunoscore and budding stratified survival from 100 to 70% and from 91 to 56%, respectively. The Glasgow Microenvironment Score, a score based on KM grade and TSP, stratified survival from 93 to 58%.
conclusions: Although associated with increasing T stage, local and systemic tumour environment characteristics, and in particular Immunoscore, budding, TSP and mGPS, are stage-independent determinants of survival and may be utilised in the staging of patients with primary operable colorectal cancer
Photon echo studies of photosynthetic light harvesting
The broad linewidths in absorption spectra of photosynthetic complexes obscure information related to their structure and function. Photon echo techniques represent a powerful class of time-resolved electronic spectroscopy that allow researchers to probe the interactions normally hidden under broad linewidths with sufficient time resolution to follow the fastest energy transfer events in light harvesting. Here, we outline the technical approach and applications of two types of photon echo experiments: the photon echo peak shift and two-dimensional (2D) Fourier transform photon echo spectroscopy. We review several extensions of these techniques to photosynthetic complexes. Photon echo peak shift spectroscopy can be used to determine the strength of coupling between a pigment and its surrounding environment including neighboring pigments and to quantify timescales of energy transfer. Two-dimensional spectroscopy yields a frequency-resolved map of absorption and emission processes, allowing coupling interactions and energy transfer pathways to be viewed directly. Furthermore, 2D spectroscopy reveals structural information such as the relative orientations of coupled transitions. Both classes of experiments can be used to probe the quantum mechanical nature of photosynthetic light-harvesting: peak shift experiments allow quantification of correlated energetic fluctuations between pigments, while 2D techniques measure quantum beating directly, both of which indicate the extent of quantum coherence over multiple pigment sites in the protein complex. The mechanistic and structural information obtained by these techniques reveals valuable insights into the design principles of photosynthetic light-harvesting complexes, and a multitude of variations on the methods outlined here
Dysregulation of the transcription factors SOX4, CBFB and SMARCC1 correlates with outcome of colorectal cancer
The aim of this study was to identify deregulated transcription factors (TFs) in colorectal cancer (CRC) and to evaluate their relation with the recurrence of stage II CRC and overall survival. Microarray-based transcript profiles of 20 normal mucosas and 424 CRC samples were used to identify 51 TFs displaying differential transcript levels between normal mucosa and CRC. For a subset of these we provide in vitro evidence that deregulation of the Wnt signalling pathway can lead to the alterations observed in tissues. Furthermore, in two independent cohorts of microsatellite-stable stage II cancers we found that high SOX4 transcript levels correlated with recurrence (HR 2.7; 95% CI, 1.2–6.0; P=0.01). Analyses of ∼1000 stage I–III adenocarcinomas, by immunohistochemistry, revealed that patients with tumours displaying high levels of CBFB and SMARCC1 proteins had a significantly better overall survival rate (P=0.0001 and P=0.0275, respectively) than patients with low levels. Multivariate analyses revealed that a high CBFB protein level was an independent predictor of survival. In conclusion, several of the identified TFs seem to be involved in the progression of CRC
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