Relationships Between the Performance of Time/Frequency Standards and Navigation/Communication Systems

The relationship between system performance and clock or oscillator performance is discussed. Tradeoffs discussed include: short term stability versus bandwidth requirements; frequency accuracy versus signal acquisition time; flicker of frequency and drift versus resynchronization time; frequency precision versus communications traffic volume; spectral purity versus bit error rate, and frequency standard stability versus frequency selection and adjustability. The benefits and tradeoffs of using precise frequency and time signals are various levels of precision and accuracy are emphasized

On the existence of effective potentials in time-dependent density functional theory

We investigate the existence and properties of effective potentials in time-dependent density functional theory. We outline conditions for a general solution of the corresponding Sturm-Liouville boundary value problems. We define the set of potentials and v-representable densities, give a proof of existence of the effective potentials under certain restrictions, and show the set of v-representable densities to be independent of the interaction.Comment: 13 page

Evidence for a dynamic phase transition in [Co/Pt]_3 magnetic multilayers

A dynamic phase transition (DPT) with respect to the period P of an applied alternating magnetic field has been observed previously in numerical simulations of magnetic systems. However, experimental evidence for this DPT has thus far been limited to qualitative observations of hysteresis loop collapse in studies of hysteresis loop area scaling. Here, we present significantly stronger evidence for the experimental observation of this DPT, in a [Co(4 A)/Pt(7 A)]_3-multilayer system with strong perpendicular anisotropy. We applied an out-of-plane, time-varying (sawtooth) field to the [Co/Pt]_3 multilayer, in the presence of a small additional constant field, H_b. We then measured the resulting out-of-plane magnetization time series to produce nonequilibrium phase diagrams (NEPDs) of the cycle-averaged magnetization, Q, and its variance, Var(Q), as functions of P and H_b. The experimental NEPDs are found to strongly resemble those calculated from simulations of a kinetic Ising model under analagous conditions. The similarity of the experimental and simulated NEPDs, in particular the presence of a localized peak in the variance Var(Q) in the experimental results, constitutes strong evidence for the presence of this DPT in our magnetic multilayer samples. Technical challenges related to the hysteretic nature and response time of the electromagnet used to generate the time-varying applied field precluded us from extracting meaningful critical scaling exponents from the current data. However, based on our results, we propose refinements to the experimental procedure which could potentially enable the determination of critical exponents in the future.Comment: substantial revision; 26 pages, 9 figures; to appear in Phys. Rev.

The correlation between ovule quality parameters and the seed yield at Cyclamen persicum MILL.

Are there indicators that the seed yield at Cyclamen persicum is predetermined by the quality of ovules? This was the main question of these investigations.The aim of our study was to investigate why only some of the available ovules develop into mature seeds. We surmised that the quality of the ovules played an important role in this. In order to corroborate this theory, we examined specific ovule parameters and their correlation with seed yield.The parameters included the levels of callose in the nucellus, the heterogeneity of embryo sacs, the deviants in callose inclusion and the number of ovules examined by light and fluorescence microscopy.There is still considerable disagreement on the biological significance of the inclusion of callose in ovules. In our study, we were able to show that the inclusion of callose is essential for fertilization in the case of C. persicum. This appears to contradict the findings reported for other plant species, where the inclusion of callose has been evaluated as a sign of ovule degeneration. However, the results of our study clearly demonstrate that seed yield is already determined by the maternal plant during the ovule development phase, i. e. shortly before and at the beginning of anthesis.Some ovule parameters allow predictions to be made about the expected seed yield for the studied genotypes of C. persicum

Comment on "Quantum mechanics of smeared particles"

In a recent article, Sastry has proposed a quantum mechanics of smeared particles. We show that the effects induced by the modification of the Heisenberg algebra, proposed to take into account the delocalization of a particle defined via its Compton wavelength, are important enough to be excluded experimentally.Comment: 2 page

The ambivalence of personal control over indoor climate - How much personal control is adequate?

Literature sets personal control over indoor environmental conditions in relation to the gap between predicted and actual energy use, the gap between predicted and observed user satisfaction, and health aspects. A focus on building energy performance often leads to the proposal of more automated and less occupant control of the indoor environment. However, a high degree of personal control is desirable because research shows that a low degree (or no) personal control highly correlates with indoor environmental dissatisfaction and sick building syndrome symptoms. These two tendencies seem contradictory and optimisation almost impossible. Based on current efficiency classes describing the effect of room automation systems on building energy use during operation, fundamental thoughts related to thermophysiology and control, recent laboratory experiments, important lessons learnt from post-occupancy studies, and documented conceptual frameworks on the level of control perceived, we discuss the ambivalence of personal control and how much personal control is adequate. Often-proposed solutions ranging from fully automated controls, over manual controls to dummy controls are discussed according to their effect on a) building energy use during operation and b) occupants perceived control. The discussion points to the importance of adequate personal control. In order to meet the goals for nearly zero energy buildings and for a human-centric design, there is the need to establish design procedures for adequate personal control as part of the design process

Three-dimensional Vorticity Effects on Extinction Behavior of Laminar Flamelets

A recently proposed rotational flamelet model (Sirignano [1, 2, 3]) is developed and tested in an improved framework of detailed chemistry and transport models. The rotational flamelet model, in contrast to standard two-dimensional or axisymmetric irrotational models, incorporates the effects of shear strain and vorticity on local flame behavior and is three-dimensional by nature. A similarity solution (Sirignano [1, 2, 3]) is used to reduce the three-dimensional governing equations to a set of ODEs involving a transformation to a non-Newtonian reference frame. Multiple flamelet cases including both diffusion and premixed flames are tested to demonstrate the impact of vorticity on flame structure, extinction, and local mixture composition. For diluted hydrogen flames where the location of minimum density coincides with the location of peak temperature, the centrifugal force induced by vorticity reduces mass flow rate in the flame zone, effectively lowering the local strain rate. This results in increased residence time, thus extending flammability limits and reducing burning rates. For pure hydrogen-oxygen flames where minimum density lies between the flame zone and the fuel inlet boundary, centrifugal forces do not significantly modify flame behavior. Stable and unstable branches of extinction curves (S-curves) are computed which showcase how vorticity extends flammability limits. These capabilities of the rotational flamelet model reveal that vital physics are currently missing from two-dimensional, irrotational, constant-density flamelet models. The improvements noted regarding detailed chemical kinetics, transport formulation, and thermo-physical properties bring the new flamelet model to par in these areas with existing models, while surpassing existing models in terms of physical emulation