Ovenless, small-size, low-power, IMU/quartz-oscillator ensemble performs like atomic clocks

The precise measurement of time has been a goal of physicists for centuries. With every new increase in our ability to measure time we have discovered new phenomena. The most advanced clocks available to us currently are atomic clocks that use electronic transitions to track the passage of time. In this proposal, I put forward the framework for the first nuclear clock estimated to be 1000 to 10000 times more precise than the current atomic clocks. This research will explore in detail the atomic nuclear interactions and help perfect and refine current atomic-nuclear interaction models. The realization of a {sup 229}Th nuclear clock will allow tests of cosmology by measuring the change of the fine structure constant as a function of time. The results of these experiments could dramatically alter our view of the universe, its past and future evolution. Precision clocks - with fundamental physics applications - require a long-lived quantum transition (two-level system) that is immune to external perturbations. Nuclear transitions would be better suited than atomic transitions for these applications except that nuclear transitions are typically much higher in energy and therefore cannot be accessed with table-top lasers. There is, however, one promising nuclear transition: the doublet between the ground and first excited states of the {sup 229}Th nucleus discovered by Helmer and Reich. This doublet has an energy splitting of 7.6 {+-} 0.5 eV, a spin difference of 1 h-bar, and an excited state half-life that could be as long as hours. A precision clock based on the {sup 229}Th nuclear doublet has been proposed by Peik et al. Their design is similar to the ion clock research being conducted at NIST in Boulder, CO. However, the NIST researchers use atomic transitions for their frequency standards. In the {sup 229}Th nuclear doublet transition is the frequency standard while atomic transitions are used to cool the ions and for probing the state of the {sup 229}Th nucleus. Recently, Campbell et al. have trapped and cooled {sup 232}Th{sup 3+} at Georgia Institute of Technology. This is a large step forward in the realization of a nuclear clock. The Georgia Tech group is already a collaborator on this project and we are in discussions with the NIST Boulder group about collaboration. In order to determine the suitability of the {sup 229}Th nuclear doublet for a precision clock, the half-life of the excited-state needs to be measured. Current estimates of the half-life vary from 10 {micro}s to 1000 hours. The longer the half-life, the narrower the natural linewidth of the state and the more desirable the transition is for potential applications. In this proposal, I outline the necessary research to be conducted to determine the half-life and exact wavelength of the nuclear doublet transition in {sup 229}Th. This research will lead to a deeper understanding of atomic-nuclear interactions important for our knowledge of high energy density science. It will provide a spectroscopy measurement of the lowest known nuclear transition ever and open the doorway for the development of a nuclear clock with unprecedented precision.

We estimate the attenuation around Cajon Pass, southern California, for frequencies above 10 Hz, and we find total Q to exhibit only weak frequency dependence, ranging from ∼800 at 10 Hz to ∼1500 at 100 Hz. The intrinsic attenuation is approximately twice the level of the scattering attenuation. Measurements are made using earthquake seismograms recorded at 0–3 km depth using the multiple lapse time window method. The results are not dependent on receiver depth and are consistent with previous estimates of Q made from direct waves recorded at 2.5 km depth. Our Q values are therefore thought to be representative of the seismogenic crust, and the technique used is uncontaminated by the highly attenuating near surface, at least above ∼10 Hz. We also calculate Q from surface data between 1 and 10 Hz and find a clear change in the frequency dependence of both intrinsic and scattering attenuation at ∼10 Hz. Q exhibits strong frequency dependence below 10 Hz ( ∝ƒ1.8), consistent with previous studies in active tectonic regions, and only weak frequency dependence at higher frequencies ( ∝ƒ0.34). This change in behavior renders it unwise to extrapolate Q measurements outside the frequency range from which they were derived, for example, in earthquake‐source studies. Possible factors responsible for the apparent change in frequency dependence of Q are considered. Further work is required, however, to resolve the causes of this change.

Markram and Tsodyks, by showing that the elevated synaptic efficacy observed with single-pulse long-term potentiation (LTP) measurements disappears with higher-frequency test pulses, have critically challenged the conventional assumption that LTP reflects a general gain increase. This observed change in frequency dependence during synaptic potentiation is called redistribution of synaptic efficacy (RSE). RSE is here seen as the local realization of a global design principle in a neural network for pattern coding. The underlying computational model posits an adaptive threshold rather than a multiplicative weight as the elementary unit of long-term memory. A distributed instar learning law allows thresholds to increase only monotonically, but adaptation has a bidirectional effect on the model postsynaptic potential. At each synapse, threshold increases implement pattern selectivity via a frequency-dependent signal component, while a complementary frequency-independent component nonspecifically strengthens the path. This synaptic balance produces changes in frequency dependence that are robustly similar to those observed by Markram and Tsodyks. The network design therefore suggests a functional purpose for RSE, which, by helping to bound total memory change, supports a distributed coding scheme that is stable with fast as well as slow learning. Multiplicative weights have served as a cornerstone for models of physiological data and neural systems for decades. Although the model discussed here does not implement detailed physiology of synaptic transmission, its new learning laws operate in a network architecture that suggests how recently discovered synaptic computations such as RSE may help produce new network capabilities such as learning that is fast, stable, and distributed.

Resonant oscillators with stable frequencies and large quality factors help us to keep track of time with high precision. Examples range from quartz crystal oscillators in wristwatches to atomic oscillators in atomic clocks, which are, at present, our most precise time measurement devices1. The search for more stable and convenient reference oscillators is continuing2–6. Nuclear oscillators are better than atomic oscillators because of their naturally higher quality factors and higher resilience against external perturbations7–9. One of the most promising cases is an ultra-narrow nuclear resonance transition in 45Sc between the ground state and the 12.4-keV isomeric state with a long lifetime of 0.47 s (ref. 10). The scientific potential of 45Sc was realized long ago, but applications require 45Sc resonant excitation, which in turn requires accelerator-driven, high-brightness X-ray sources11 that have become available only recently. Here we report on resonant X-ray excitation of the 45Sc isomeric state by irradiation of Sc-metal foil with 12.4-keV photon pulses from a state-of-the-art X-ray free-electron laser and subsequent detection of nuclear decay products. Simultaneously, the transition energy was determined as {mathrm{12,389.59}}_{+0.12left({rm{syst}}right)}^{pm 0.15left({rm{stat}}right)},{rm{eV}} with an uncertainty that is two orders of magnitude smaller than the previously known values. These advancements enable the application of this isomer in extreme metrology, nuclear clock technology, ultra-high-precision spectroscopy and similar applications.

A study is made of the various aspects of the algorithm theoretically, comparing the NBS (US National Bureau of Standards) algorithm with a Kalman filter to discuss questions of optimality. It is shown that since the time of a clock is not measured, but only the time difference between clocks, a time scale should not attempt to optimize time accuracy, since that has no meaning. However, time uniformity and frequency stability can be optimized. The authors further study the practice of monitoring the clocks in a time scale for frequency steps, and removing a clock from the scale when a step has been detected until the new frequency is learned. The authors show that the effect of this practice on the algorithm is to translate random walk behavior in the individual clocks, due to the frequency steps of the clocks, to flicker noise for the ensemble. The implication is that careful monitoring of the scale can significantly improve its long-term performance.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

In order to ensure the long-term stability of the time scale, the traditional timekeeping clock ensemble is mainly composed of a cesium clock and a few hydrogen masers. Since 2014, the Bureau International des Poids et Mesures (BIPM) has changed the weighting method of atomic clocks, using the predictability of atomic clocks to weight the global atomic clocks to obtain the International Atomic Time (TAI) and Coordinated Universal Time (UTC). Because of the good predictability of hydrogen masers, less than one third of the number of atomic clocks in TAI/UTC calculation is hydrogen masers which has gained 75% weight. Effective utilization of hydrogen masers has become a research hotspot in timekeeping laboratories. In order to give full play to the advantages of hydrogen masers in timekeeping, the time scale of hydrogen masers is tested in this paper. Firstly, the frequency drift parameters of hydrogen masers are dynamically estimated by using the minimum error theory. Then the estimated parameters are applied to a real-time exponential filtering time scale algorithm. The results show that the stability of the time scale produced by this method can reach 6e-15/day, and the absolute maximum deviation from TA(NTSC) within a month can be kept within 5 ns, which is better than the time scales produced by a traditional fixed frequency drift parameters method and the classical weighted averaging algorithm ALGOS.

A high performance Space-Time Reference in orbit could be realized using a\nstable atomic clock in a precisely defined orbit and linking that to high\naccuracy atomic clocks on the ground using a laser based time-transfer link.\nThis would enhance performance of existing systems and provide unique\ncapabilities in navigation, precise timing, earth sciences, geodesy and the\nsame approach could provide a platform for testing fundamental physics in\nspace. Precise laser time- and frequency-transfer from the ground to an\norbiting satellite would make it possible to improve upon the current state of\nthe art in timing (about 1 to 30 ns achieved with GPS) by roughly a factor of\n1000 to the 1 ps level.\n

Precision Clocks in Space and α-Variations

The manufacture and properties of novel glass electrodes with solid-state contacts are described. The electrodes consist of spherical electrode membranes made of two different kinds of glass. The thin membrane in contact with the measured medium consists of an ion-selective electrolytically conducting material such as pH or pNa glass, whereas the other glass is a mixed Conducton This latter part of the double membrane uses electron- and ion-conducting mechanisms and is silver-coated. The mixed conduction glass and its metallic coating together form the internal discharge system of the ion-selective electrode. Investigation of the electrode function and the stability of its potendal has shown that its measuring characterisdcs are substantially better than those of glass electrodes with an internally metal-coated membrane. The reason for this is that reversible Charge carrier transitions (redox reactions) are possible at all phase boundaries. The electron transition is brought about by a change in the conduction mechanism from ionic conduction to electronic conduction. From the position of the isotherm intersection points outside the utilizable measuring ränge of the electrodes, it follows that automatic temperature compensation is not possible.

Moisture content is a critical parameter in the performance of road materials, influencing compaction, stability, and long-term durability. Traditional gravimetric methods, such as oven-drying, provide accurate reference values but are too slow for effective field quality control (QC). This study evaluates two portable dielectric-based devices, the AquaProbe and the MicroLance, for their applicability in instant determination of moisture content in road construction materials. A literature review combined with laboratory experiments on clayey soil, silty sand, sandy soil, recycled construction material, base course aggregates, and forest road materials provided a comparative basis. The AquaProbe, which applies time/frequency domain dielectric measurement, was calibrated using oven-dried samples and demonstrated strong linear correlations (R² = 0.94–0.96) between direct readings and actual moisture content, particularly reliable in fine-grained soils. The MicroLance, based on capacitance sensing with automatic temperature compensation and rapid in-field calibration, showed logarithmic correlations (R² = 0.93–0.98) and proved especially effective for coarse-grained and recycled materials. Both instruments highlighted moisture measurement sensitivity to material type, and compaction state. Findings suggest a dual strategy for practical use: MicroLance as a rapid screening tool in granular and recycled materials, and AquaProbe for dual monitoring and verification, especially in cohesive soils. With appropriate calibration, both devices can significantly increase efficiency, accuracy, and time savings in road construction quality control, reducing risks related to poor compaction and extending pavement life.

A Local-Control Model of the Guinea Pig Ventricular Myocyte Allows Understanding of Force-Interval Relations at the Calcium Spark Level

The effect of transient anoxia on the cochlear microphonic potential at different sound frequencies was investigated. The microphonic potential was recorded with glass microelectrodes in the ductus cochlearis of the pigeon ear. Transient anoxia had different effects, related to frequency, on the amplitude and the relative phase angle of the microphonic potential recorded from one place in the ductus cochlearis. At frequencies equal to and higher than the best frequency the amplitude of the microphonic potential was more sensitive to anoxia than it was at lower frequencies. Microphonic potential at 1 kHz lower than the best frequency was often enlarged in amplitude during transient anoxia. The results suggest that this frequency-dependent effect is a positional one. Changes in the phase were largest around the best frequency. It is inferred that anoxia causes complex changes in the pattern of vibration in the cochlear partition. The observed changes in amplitude and also changes in phase are caused by the combined effects of reduction of the endolymphatic potential and changes in vibration pattern.

In this paper partial discharges (PD) in a disc-shaped cavity are measured at variable frequency (0.01 - 100 Hz) of the applied voltage. The measured PD phase and magnitude distributions, as well as the number of PDs per voltage cycle, changed with the varying frequency. A charge consistent model is presented and used to dynamically simulate the sequence of PDs in the cavity. The simulation results show that the properties of the cavity surface, mainly the surface conductivity and the surface emission of electrons, change with the varying applied frequency. This is interpreted as an effect of the difference in time between consecutive PDs at different applied frequencies. This is the second of two papers addressing the frequency dependence of PD in a cavity. The first paper described how the PD frequency dependence changes with the applied voltage amplitude, the cavity size and the cavity location.

Sleep deprivation (SD) adversely affects brain function and is accompanied by frequency dependent changes in EEG. Recent studies have suggested that BOLD fluctuations pertain to a spatiotemporal organization with different frequencies. The present study aimed to investigate the frequency-dependent SD-related brain oscillatory activity by using the amplitude of low-frequency fluctuation (ALFF) analysis. The ALFF changes were measured across different frequencies (Slow-4: 0.027–0.073 Hz; Slow-5: 0.01–0.027 Hz; and Typical band: 0.01–0.08 Hz) in 24 h SD as compared to rested wakeful during resting-state fMRI. Sixteen volunteers underwent two fMRI sessions, once during rested wakefulness and once after 24 h of SD. SD showed prominently decreased ALFF in the right inferior parietal lobule (IPL), bilateral orbitofrontal cortex (OFC) and dorsolateral prefrontal cortex (DLPFC), while increased ALFF in the visual cortex, left sensorimotor cortex and fusiform gyrus. Across the Slow-4 and Slow-5, results differed significantly in the OFC, DLPFC, thalamus and caudate in comparison to typical frequency band; and Slow-4 showed greater differences. In addition, negative correlations of behavior performance and ALFF patterns were found mainly in the right IPL across the typical frequency band. These observations provided novel insights about the physiological responses of SD, identified how it disturbs the brain rhythms, and linked SD with frequency-dependent alterations in amplitude patterns.

A comparison among three precise timing centers in the United States has been conducted for more than 1 year using three different synchronization methods. The timing centers involved were the United States Naval Observatory (USNO) in Washington, DC, Newark Air Force Station (NAFS) in Newark, Ohio, and the National Bureau of Standards (NBS) in Boulder, Colorado. The three methods were cesium beam portable clocks; Loran-C transmissions from Cape Fear, North Carolina, and Dana, Indiana; and ABC, CBS, and NBC network television broadcasts commonly received by the three timing centers.Cesium beam portable clocks have the capability of accurately and precisely synchronizing remote clocks to within 0.1 μs. The Loran-C data involved a 3500 km (2180 miles) ground wave path – the longest Loran-C ground wave path that has been studied with the precision and accuracy reported herein. The long-term precision achieved was about 1 μs over 1 year. The accuracy is limited on occasion by inability to resolve the 10 μs ambiguity of the 100-kHz pulse train. The precision capability of maintaining remote clock synchronization within the majority of the continental United States using network television broadcasts was inferred to be about 5 ns·τ1/3 s-1/3 over the range of τ from 86 400 s (1 day) to about 107 s (324 days) but with definite accuracy limitations caused by such factors as occasional network re-routing of the television signals. Some estimates of the long-term frequency stabilities among the references used at the three timing centers were measured or inferred.