108 research outputs found
Stepwise drying of Lake Turkana at the end of the African Humid Period: a forced regression modulated by solar activity variations?
Although the timing of the termination of the
African Humid Period (AHP) is now relatively well estab-
lished, the modes and controlling factors of this drying are
still debated. Here, through a geomorphological approach,
we characterize the regression of Lake Turkana at the end
of the AHP. We show that lake level fall during this period
was not continuous but rather stepwise and consisted of five
episodes of rapid lake level fall separated by episodes marked
by slower rates of lake level fall. Whereas the overall regres-
sive trend reflects a decrease in regional precipitations linked
to the gradual reduction in Northern Hemisphere summer in-
solation, itself controlled by orbital precession, we focus dis-
cussion on the origin of the five periods of accelerated lake
level fall. We propose that these periods are due to temporary
reductions in rainfall across the Lake Turkana area associ-
ated with repeated westward displacement of the Congo Air
Boundary (CAB) during solar activity minima
Visible Photolysis and Amperometric Detection of S -Nitrosothiols
The concentration of S-nitrosothiols (RSNOs), endogenous transporters of the signaling molecule nitric oxide (NO), fluctuate greatly in physiology often as a function of disease state. RSNOs may be measured indirectly by cleaving the SâN bond and monitoring the liberated NO. While ultraviolet photolysis and reductive-based cleavage both decompose RSNOs to NO, poor selectivity and the need for additional reagents preclude their utility clinically. Herein, we report the coupling of visible photolysis (i.e., 500â550 nm) and amperometric NO detection to quantify RSNOs with greater selectivity and sensitivity. Enhanced sensitivity (up to 1.56 nA ”Mâ1) and lowered theoretical detection limits (down to 30 nM) were achieved for low molecular weight RSNOs (i.e., S-nitrosoglutathione, S-nitrosocysteine) by tuning the irradiation exposure. Detection of nitrosated proteins (i.e., S-nitrosoalbumin) was also possible, albeit at a decreased sensitivity (0.11 nA ”Mâ1). This detection scheme was used to measure RSNOs in plasma and illustrate the potential of this method for future physiological studies
Quantum modulation of a coherent state wavepacket with a single electron spin
The interaction of quantum objects lies at the heart of fundamental quantum
physics and is key to a wide range of quantum information technologies.
Photon-quantum-emitter interactions are among the most widely studied.
Two-qubit interactions are generally simplified into two quantum objects in
static well-defined states . In this work we explore a fundamentally new
dynamic type of spin-photon interaction. We demonstrate modulation of a
coherent narrowband wavepacket with another truly quantum object, a quantum dot
with ground state spin degree of freedom. What results is a quantum modulation
of the wavepacket phase (either 0 or {\pi} but no values in between), a new
quantum state of light that cannot be described classically.Comment: Supplementary Information available on reques
Efficient Interpolation for the Theory of Arrays
Existing techniques for Craig interpolation for the quantifier-free fragment
of the theory of arrays are inefficient for computing sequence and tree
interpolants: the solver needs to run for every partitioning of the
interpolation problem to avoid creating -mixed terms. We present a new
approach using Proof Tree Preserving Interpolation and an array solver based on
Weak Equivalence on Arrays. We give an interpolation algorithm for the lemmas
produced by the array solver. The computed interpolants have worst-case
exponential size for extensionality lemmas and worst-case quadratic size
otherwise. We show that these bounds are strict in the sense that there are
lemmas with no smaller interpolants. We implemented the algorithm and show that
the produced interpolants are useful to prove memory safety for C programs.Comment: long version of the paper at IJCAR 201
Determination of the LOQ in real-time PCR by receiver operating characteristic curve analysis: application to qPCR assays for Fusarium verticillioides and F. proliferatum
Real-time PCR (qPCR) is the principal technique for the quantification of pathogen biomass in host tissue, yet no generic methods exist for the determination of the limit of quantification (LOQ) and the limit of detection (LOD) in qPCR. We suggest using the Youden index in the context of the receiver operating characteristic (ROC) curve analysis for this purpose. The LOQ was defined as the amount of target DNA that maximizes the sum of sensitivity and specificity. The LOD was defined as the lowest amount of target DNA that was amplified with a false-negative rate below a given threshold. We applied this concept to qPCR assays for Fusarium verticillioides and Fusarium proliferatum DNA in maize kernels. Spiked matrix and field samples characterized by melting curve analysis of PCR products were used as the source of true positives and true negatives. On the basis of the analysis of sensitivity and specificity of the assays, we estimated the LOQ values as 0.11Â pg of DNA for spiked matrix and 0.62Â pg of DNA for field samples for F. verticillioides. The LOQ values for F. proliferatum were 0.03Â pg for spiked matrix and 0.24Â pg for field samples. The mean LOQ values correspond to approximately eight genomes for F. verticillioides and three genomes for F. proliferatum. We demonstrated that the ROC analysis concept, developed for qualitative diagnostics, can be used for the determination of performance parameters of quantitative PCR
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