409 research outputs found
Iron Deprivation in Synechocystis : Inference of Pathways, Non-coding RNAs, and Regulatory Elements from Comprehensive Expression Profiling
Iron is an essential cofactor in many metabolic reactions. Mechanisms controlling iron homeostasis need to respond rapidly to changes in extracellular conditions, but they must also keep the concentration of intracellular iron under strict control to avoid the generation of damaging reactive oxygen species. Due to its role as a redox carrier in photosynthesis, the iron quota in cyanobacteria is about 10 times higher than in model enterobacteria. The molecular details of how such a high quota is regulated are obscure. Here we present experiments that shed light on the iron regulatory system in cyanobacteria. We measured time-resolved changes in gene expression after iron depletion in the cyanobacterium Synechocystis sp. PCC 6803 using a comprehensive microarray platform, monitoring both protein-coding and non-coding transcripts. In total, less than a fifth of all protein-coding genes were differentially expressed during the first 72 hr. Many of these proteins are associated with iron transport, photosynthesis, or ATP synthesis. Comparing our data with three previous studies, we identified a core set of 28 genes involved in iron stress response. Among them were genes important for assimilation of inorganic carbon, suggesting a link between the carbon and iron regulatory networks. Nine of the 28 genes have unknown functions and constitute key targets for further functional analysis. Statistical and clustering analyses identified 10 small RNAs, 62 antisense RNAs, four 59UTRs, and seven intragenic elements as potential novel components of the iron regulatory network in Synechocystis. Hence, our genome-wide expression profiling indicates an unprecedented complexity in the iron regulatory network of cyanobacteria.Portuguese Fundacao para a Ciencia e a Tecnologia (FCT) [PTDC/BIA-MIC/101036/2008]; Deutsche Forschungsgemeinschaft (DFG) Focus program "Sensory and regulatory RNAs in Prokaryotes [SPP1258]; FCT [PEst-OE/EQB/LA0023/2011]info:eu-repo/semantics/publishedVersio
Residual Kondo effect in quantum dot coupled to half-metallic ferromagnets
We study the Kondo effect in a quantum dot coupled to half-metallic
ferromagnetic electrodes in the regime of strong on-dot correlations. Using the
equation of motion technique for nonequilibrium Green functions in the slave
boson representation we show that the Kondo effect is not completely suppressed
for anti-parallel leads magnetization. In the parallel configuration there is
no Kondo effect but there is an effect associated with elastic cotunneling
which in turn leads to similar behavior of the local (on-dot) density of states
(LDOS) as the usual Kondo effect. Namely, the LDOS shows the temperature
dependent resonance at the Fermi energy which splits with the bias voltage and
the magnetic field. Moreover, unlike for non-magnetic or not fully polarized
ferromagnetic leads the only minority spin electrons can form such resonance in
the density of states. However, this resonance cannot be observed directly in
the transport measurements and we give some clues how to identify the effect in
such systems.Comment: 15 pages, 8 figures, accepted for publication in J. Phys.: Condens.
Mat
Dynamics of Bloch vectors and the channel capacity of a non identical charged qubit pair
We have considered a system of two superconducting charge qubits capacitively
coupled to a microwave resonator. The dynamics of the Bloch vectors are
investigated for different regimes. By means of the Bloch vectors and cross
dyadic we quantify the degree of entanglement contained in the generated
entangled state. We consider different values of the system parameters to
discuss the dynamics of the channel capacity between the qubits. We show that
there is an important role played by initial state settings, coupling constant
and the mean photon number on generating entangled state with high degree of
entanglement and high capacity
Andreev Reflection in Strong Magnetic Fields
We have studied the interplay of Andreev reflection and cyclotron motion of
quasiparticles at a superconductor-normal-metal interface with a strong
magnetic field applied parallel to the interface. Bound states are formed due
to the confinement introduced both by the external magnetic field and the
superconducting gap. These bound states are a coherent superposition of
electron and hole edge excitations similar to those realized in finite
quantum-Hall samples. We find the energy spectrum for these Andreev edge states
and calculate transport properties.Comment: 5 pages, 3 figures, RevTex, revised to include more detailed
discussion of currents and transpor
Practicum for international students in teacher education programs: an investigation of three university sites through multisocialisation, interculturalisation and reflection
This chapter explores the practicum experience of international students undertaking education programs at three different universities in Australia. International students were interviewed about their practicum experiences with a particular focus on what worked well and what needed improvement. Through a thematic analysis as well as identifying aspects of the interview data related to multisocialisation, interculturalisation and reflection models the authors share findings even though international students may experience difficulties during their practicum they also note that these experiences allow them to learn. When mentor teachers were able to recognise the international students’ strengths then placements were successful. Further, unpacking areas that need improvement through a supportive manner enabled students to learn and reconstruct their practice. The rich and informative data on the challenges and successful approaches across the three sites in this study add to the body of literature regarding effective ways to improve work placements for international students
Theory and practice in the construction of professional identity in nursing students: A qualitative study
The Quantum Internet
Quantum networks offer a unifying set of opportunities and challenges across
exciting intellectual and technical frontiers, including for quantum
computation, communication, and metrology. The realization of quantum networks
composed of many nodes and channels requires new scientific capabilities for
the generation and characterization of quantum coherence and entanglement.
Fundamental to this endeavor are quantum interconnects that convert quantum
states from one physical system to those of another in a reversible fashion.
Such quantum connectivity for networks can be achieved by optical interactions
of single photons and atoms, thereby enabling entanglement distribution and
quantum teleportation between nodes.Comment: 15 pages, 6 figures Higher resolution versions of the figures can be
downloaded from the following link:
http://www.its.caltech.edu/~hjkimble/QNet-figures-high-resolutio
On the role of computers in creativity-support systems
We report here on our experiences with designing computer-based creativity-support systems over several years. In particular, we present the design of three different systems incorporating different mechanisms of creativity. One of them uses an idea proposed by Rodari to stimulate imagination of the children in writing a picture-based story. The second one is aimed to model creativity in legal reasoning, and the third one uses low-level perceptual similarities to stimulate creation of novel conceptual associations in unrelated pictures.We discuss lessons learnt from these approaches, and address their implications for the question of how far creativity can be tamed by algorithmic approaches
Body size and vocalization in primates and carnivores
A fundamental assumption in bioacoustics is that large animals tend to produce vocalizations with lower frequencies than small animals. This inverse relationship between body size and vocalization frequencies is widely considered to be foundational in animal communication, with prominent theories arguing that it played a critical role in the evolution of vocal communication, in both production and perception. A major shortcoming of these theories is that they lack a solid empirical foundation: rigorous comparisons between body size and vocalization frequencies remain scarce, particularly among mammals. We address this issue here in a study of body size and vocalization frequencies conducted across 91 mammalian species, covering most of the size range in the orders Primates (n = 50; ~0.11–120 Kg) and Carnivora (n = 41; ~0.14–250 Kg). We employed a novel procedure designed to capture spectral variability and standardize frequency measurement of vocalization data across species. The results unequivocally demonstrate strong inverse relationships between body size and vocalization frequencies in primates and carnivores, filling a long-standing gap in mammalian bioacoustics and providing an empirical foundation for theories on the adaptive function of call frequency in animal communication
Shot noise in mesoscopic systems
This is a review of shot noise, the time-dependent fluctuations in the
electrical current due to the discreteness of the electron charge, in small
conductors. The shot-noise power can be smaller than that of a Poisson process
as a result of correlations in the electron transmission imposed by the Pauli
principle. This suppression takes on simple universal values in a symmetric
double-barrier junction (suppression factor 1/2), a disordered metal (factor
1/3), and a chaotic cavity (factor 1/4). Loss of phase coherence has no effect
on this shot-noise suppression, while thermalization of the electrons due to
electron-electron scattering increases the shot noise slightly. Sub-Poissonian
shot noise has been observed experimentally. So far unobserved phenomena
involve the interplay of shot noise with the Aharonov-Bohm effect, Andreev
reflection, and the fractional quantum Hall effect.Comment: 37 pages, Latex, 10 figures (eps). To be published in "Mesoscopic
Electron Transport," edited by L. P. Kouwenhoven, G. Schoen, and L. L. Sohn,
NATO ASI Series E (Kluwer Academic Publishing, Dordrecht
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