Accurate timekeeping is controlled by a cycling activator in Arabidopsis.

Transcriptional feedback loops are key to circadian clock function in many organisms. Current models of the Arabidopsis circadian network consist of several coupled feedback loops composed almost exclusively of transcriptional repressors. Indeed, a central regulatory mechanism is the repression of evening-phased clock genes via the binding of morning-phased Myb-like repressors to evening element (EE) promoter motifs. We now demonstrate that a related Myb-like protein, REVEILLE8 (RVE8), is a direct transcriptional activator of EE-containing clock and output genes. Loss of RVE8 and its close homologs causes a delay and reduction in levels of evening-phased clock gene transcripts and significant lengthening of clock pace. Our data suggest a substantially revised model of the circadian oscillator, with a clock-regulated activator essential both for clock progression and control of clock outputs. Further, our work suggests that the plant clock consists of a highly interconnected, complex regulatory network rather than of coupled morning and evening feedback loops. DOI:http://dx.doi.org/10.7554/eLife.00473.001

System clock estimation based on clock wastage minimization

When synthesizing a hardware implementation from behavioral descriptions, an important decision is the selection of a clock cycle to schedule the datapath operations into control steps. Most existing behavioral synthesis systems either require the designer to specify the clock cycle explicitly or require that the delays of the operators used in the design be specified in multiples of a clock cycle. In the absence of any tool to guide the selection of a clock cycle, a bad choice of the clock period could adversely affect the performance of the synthesized design. We present an algorithm for estimating the system clock based on a clock wastage minimization criteria. Limitations of previous approaches to the problem are discussed. The results obtained prove that the clock cycle estimated by the Clock Wastage Minimization method produce faster designs than previous solutions to the problem

Gravitomagnetism and Relative Observer Clock Effects

The gravitomagnetic clock effect and the Sagnac effect for circularly rotating orbits in stationary axisymmetric spacetimes are studied from a relative observer point of view, clarifying their relationships and the roles played by special observer families. In particular Semer\'ak's recent characterization of extremely accelerated observers in terms of the two-clock clock effect is shown to be complemented by a similarly special property of the single-clock clock effect.Comment: 19 pages, LaTeX, IOP macros with package epsf and 1 eps figure, to appear in Classical and Quantum Gravity, slight revisio

Thyroxine differentially modulates the peripheral clock: lessons from the human hair follicle

The human hair follicle (HF) exhibits peripheral clock activity, with knock-down of clock genes (BMAL1 and PER1) prolonging active hair growth (anagen) and increasing pigmentation. Similarly, thyroid hormones prolong anagen and stimulate pigmentation in cultured human HFs. In addition they are recognized as key regulators of the central clock that controls circadian rhythmicity. Therefore, we asked whether thyroxine (T4) also influences peripheral clock activity in the human HF. Over 24 hours we found a significant reduction in protein levels of BMAL1 and PER1, with their transcript levels also decreasing significantly. Furthermore, while all clock genes maintained their rhythmicity in both the control and T4 treated HFs, there was a significant reduction in the amplitude of BMAL1 and PER1 in T4 (100 nM) treated HFs. Accompanying this, cell-cycle progression marker Cyclin D1 was also assessed appearing to show an induced circadian rhythmicity by T4 however, this was not significant. Contrary to short term cultures, after 6 days, transcript and/or protein levels of all core clock genes (BMAL1, PER1, clock, CRY1, CRY2) were up-regulated in T4 treated HFs. BMAL1 and PER1 mRNA was also up-regulated in the HF bulge, the location of HF epithelial stem cells. Together this provides the first direct evidence that T4 modulates the expression of the peripheral molecular clock. Thus, patients with thyroid dysfunction may also show a disordered peripheral clock, which raises the possibility that short term, pulsatile treatment with T4 might permit one to modulate circadian activity in peripheral tissues as a target to treat clock-related disease

Processing circuit with asymmetry corrector and convolutional encoder for digital data

A processing circuit is provided for correcting for input parameter variations, such as data and clock signal symmetry, phase offset and jitter, noise and signal amplitude, in incoming data signals. An asymmetry corrector circuit performs the correcting function and furnishes the corrected data signals to a convolutional encoder circuit. The corrector circuit further forms a regenerated clock signal from clock pulses in the incoming data signals and another clock signal at a multiple of the incoming clock signal. These clock signals are furnished to the encoder circuit so that encoded data may be furnished to a modulator at a high data rate for transmission

Collisional losses, decoherence, and frequency shifts in optical lattice clocks with bosons

We have quantified collisional losses, decoherence and the collision shift in a one-dimensional optical lattice clock with bosonic 88Sr. The lattice clock is referenced to the highly forbidden transition 1S0 - 3P0 at 698 nm, which becomes weakly allowed due to state mixing in a homogeneous magnetic field. We were able to quantify three decoherence coefficients, which are due to dephasing collisions, inelastic collisions between atoms in the upper and lower clock state, and atoms in the upper clock state only. Based on the measured coefficients, we determine the operation parameters at which a 1D-lattice clock with 88Sr shows no degradation due to collisions on the relative accuracy level of 10-16.Comment: 4 pages, 3 figure

Curriculum sequencing and the acquisition of clock reading skills among Chinese and Flemish children

The present study reexamines the adoption of clock reading skills in the primary mathematics curriculum. In many Western countries, the mathematics curriculum adopts a number of age-related stages for teaching clock reading skills, that were defined by early research (e.g., Friedman & laycock, 1989; Piaget, 1969). Through a comparison of Flemish and Chinese student’s clock reading abilities, the current study examines whether these age-related stages are a solid base for teaching clock reading skills. By means of both quantitative (ANOVA’s) and qualitative (textbook analysis) methods, the present study indicates that the alternative way of teaching clock reading skills in China, i.e., at the age of six instead of staggered out over several grades, results in a two years earlier acquisition of clock reading skills. This indicates that the previously age-related stages in children’s acquisition of clock reading are not universal, nor the most effective way to teach these skills to young children