考虑非牛顿引力下的快速转动混合星性质

计算和讨论了考虑非牛顿引力下的快速转动混合星结构与性质,包括质量-半径关系、Kepler转速、转动惯量、引力红移以及转动动能和引力结合能之比等.结果表明,转动将有效地增大混合星能支持的最大质量,Kepler转速下能支持的最大质量比静态时增加20%左右;转动对于考虑非牛顿引力的混合星整体结构性质(包括质量-半径关系、转动惯量、转动动能和引力结合能之比等)具有明显的影响,但对极向引力红移影响相对较小.     

The AEgIS antihydrogen gravity experiment

The experimental program of the AEgIS experiment at CERN’s AD complex aims to perform the first measurement of the gravitational interaction of antimatter, initially to a precision of about 1%, to ascertain the veracity of Einstein’s Weak Equivalence Principle for antimatter. As gravity is very much weaker than electromagnetic forces, such an experiment can only be done using neutral antimatter. The antihydrogen atoms also need to be very cold for the effects of gravity to be visible above the noise of thermal motion. This makes the experiment very challenging and has necessitated the introduction of several new techniques into the experimental field of antihydrogen studies, such as pulsed formation of antihydrogen via 3-body recombination with excited state positronium and the subsequent acceleration of the formed antihydrogen using electric gradients (Stark acceleration). The gravity measurement itself will be performed using a classical Moire deflectometer. Here we report on the present state of the experiment and the prospects for the near future.     

General models of Einstein gravity with a non-Newtonian weak-field limit

We investigate Einstein theories of gravity, coupled to a scalar field j{\varphi} and point-like matter, which are characterized by a scalar field-dependent matter coupling function e^H(j){e^{H(\varphi)}} . We show that under mild constraints on the form of the potential for the scalar field, there are a broad class of Einstein-like gravity models—characterized by the asymptotic behavior of H—which allow for a non-Newtonian weak-field limit with the gravitational potential behaving for large distances as ln r. The Newtonian term GM/r appears only as sub-leading. We point out that this behavior is also shared by gravity models described by f (R) Lagrangians. The relevance of our results for the building of infrared modified theories of gravity and for modified Newtonian dynamics is also discussed.     

Evidence for asymptotic safety from lattice quantum gravity

We calculate the spectral dimension for nonperturbative quantum gravity defined via Euclidean dynamical triangulations. We find that it runs from a value of ～3/2 at short distance to ～4 at large distance scales, similar to results from causal dynamical triangulations. We argue that the short-distance value of 3/2 for the spectral dimension may resolve the tension between asymptotic safety and the holographic principle.     

Evidence for muon neutrino oscillation in an accelerator-based experiment

We present results for nu(mu) oscillation in the KEK to Kamioka (K2K) long-baseline neutrino oscillation experiment. K2K uses an accelerator-produced nu(mu) beam with a mean energy of 1.3 GeV directed at the Super-Kamiokande detector. We observed the energy-dependent disappearance of nu(mu), which we presume have oscillated to nu(tau). The probability that we would observe these results if there is no neutrino oscillation is 0.0050% (4.0 sigma).     

Quantum integrals of motion and gravity wave experiment: Measurements in pure quantum states

Quantum limitations arising in measurements of a classical force acting on a quantum harmonic oscillator are studied in connection with the problem of increasing the sensitivity of gravity wave experiments. The physical nature of possible limits of sensitivity is elucidated. It originates in a degree of an uncertainty of an observable used for detecting an external force. This uncertainty can be made as small as desired for all moments of time for the observables corresponding to quantum integrals of motion. Advantages of integrals of motion with continuous spectra (like the operator of the initial coordinate) over integrals with discrete spectra (like energy) are discussed. An example of an observable suitable for exact continuous measurements of an external force independently on the initial state of the system—the difference link operator—is given. The general rule for constructing such “optimal observables” can be derived from the quantum optimal filtration theory. It is shown using Ehrenfest's theorem that no quantum limitations exist in principle for the accuracy of measurements of an external classical force acting on an arbitrary quantum system: limitations can appear only due to nonadequate measuring procedures. The general problem of finding the initial quantum states possessing the best sensitivity to an external force is formulated. The parametrically excited oscillator is briefly discussed, and it is shown that measuring the suitable integral of motion one can achieve the great gain in sensitivity. The role of quantum interference effects is emphasized.     

Gravitational waves and red shifts: A space experiment for testing relativistic gravity using multiple time-correlated radio signals

We describe an experimental technique for detecting extremely low-frequency pulses of gravitational radiation ( _GW 1–10 mHz) originating from collapsing supermassive objects (M 10⁶–10⁷ m ) occurring anywhere in the universe. Our technique is the natural outgrowth of a previous gravitational space mission. The novelty of our approach is in placing a highly stable hydrogen maser onboard a deep-space probe that controls a transmitter sending signals to earth. The spacecraft also includes a doppler transponder operating in the conventional two-way mode. Doppler tracking using simultaneously acquired one- and two-way information both on the spacecraft and at the earth station provides four time-records of frequency fluctuations. A single gravitational disturbance manifests itself as a uniquely determined pulse sequence in the two or more data sets whose amplitudes and arrival times depend on a single parameter. The repetition of the signal and the noises in the data can be used in a filtering scheme to improve the amplitude sensitivity by a factor of about 6 in amplitude (36 in energy). We believe the most likely of these gravitational pulse events occurring frequently enough to be detected (more than once per year) will come from the formation of black holes in the cores of ordinary spiral galaxies. We propose a technologically feasible and realistic space mission, using the above technique, to measure two aspects of gravitation with the same experimental equipment. The spaceflight begins in a highly eccentric earth orbit to measure the gravitational red shift and the second-order doppler effects to an accuracy of 5 parts in 10⁶; at this level significant new tests of nonmetric theories of gravity are possible. Later, the spacecraft is sent into a heliocentric orbit to distances beyond 6 AU to search for gravitational radiation.     

Thermal boundary layer for non-Newtonian fluid

Summary Analytical and numerical solutions for the momentum and thermal boundary layer equations of a non-Newtonian power law fluid are presented. The flow is assumed to be under the influence of an external magnetic fieldB (x) applied perpendicular to the surface and an electric fieldE(x) perpendicular toB(x) and the direction of the longitudinal velocity in the boundary layer. For the power law fluid it is assumed that the shear stress is proportional to then-th power of the velocity gradient andn is called the flow index. The variations of the velocity fieldf′, the temperature field θ, the shear stress on the surfaceτ _W , the displacement thicknessδ ₁ and the momentum thicknessδ ₂ with the magnetic-field parameter γ, the flow indexn, the heat transfer indexS and the Prandtl number Pr are studied. It is found that, if the outer flow velocityU(x) (potential flow) is proportional to the arc lengthx raised to a powerm, then the similarity solution for the thermal boundary layer equation is possible only whenm=1/3, which represents flow past a wedge of included angle π/2. It is established that the temperature of the wedge increases with the increase of γ, Pr,S and the decrease ofn. In general the magnetic field can be used as a heater for the surface of the wedge.     

Variational principle for flow of non-Newtonian fluids

A variational principle is formulated for finding stationary solutions of the equations of motion for an incompressible non-Newtonian fluid with constitutive equation of the Reiner-Rivlin type. The basic functional is related, but not identical to the rate of energy dissipation. It can be used for analyzing the stability of the stationary state against small perturbations.     

Evidence of internal gravity waves in the lower thermosphere at midlatitudes

Summary Wind measurements were made by the CNR Meteor Radar Station at Budrio (45°N, 12°E) in the April–September 1978 period in order to emphasize the role of internal gravity (IG) waves in the lower thermosphere ((80÷110) km). After briefly describing the basic properties of these waves, we determine some of their characteristics using both the conventional spectral-analysis methods and alternatively, for short-time data series, the maximum-entropy method (MEM). The Fourier analysis of these data indicates that the gravity waves with periods of 2<T<8 h have amplitudes increasing with height (up to (30÷40) ms⁻¹ at 100 km, in June), vertical wave-lengths of (8÷40) km and horizontal wave-lengths exceeding the corresponding ones by a factor of 50 or more. In May and September, by using the MEM method with a sampling of (10°20) min, gravity waves with periods of about 100 min and 2 h, respectively, have been tentatively identified. In August, the rates of energy loss per unit mass for internal gravity waves range from 0.015 to 0.045 W kg⁻¹ in the (80°100) km region and the momentum deposition by these waves is 2.4 m s⁻¹ h⁻¹ at 90 km. Under some specific conditions, the observed accelerations of the prevailing wind ((3÷4) m s⁻¹ d⁻¹) due to momentum deposition over a period of 4 consecutive days (24–27 August) may approach the above-calculated maximum value.

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Riassunto Misure di vento effettuate presso la Stazione Radar Meteorica del CNR di Budrio (45°N, 12°E) nel periodo aprile-settembre 1978 consentono di mettere in evidenza il ruolo delle onde interne di gravità (IG) nella bassa termosfera ((80÷110) km). Dopo aver descritto brevemente le proprietà basilari di tali onde, sono state determinate alcune loro caratteristiche facendo ricorso sia ai metodi tradizionali dell'analisi spettrale sia, in alternativa, per serie con un numero limitato di dati, al metodo della massima entropia (MEM). L'analisi di Fourier indica che le onde di gravità con periodo tra 2 e 8 ore hanno ampiezza crescente con l'altezza (fino a (30÷40) m s⁻¹ a 100 km in giugno), lunghezze d'onda verticali di (8÷40) km e orizzontali che superano le corrispondenti verticali di un fattore 50 o più. In maggio e settembre, facendo ricorso al metodo MEM e raggruppando i dati ogni (10÷20) min, sono state identificate, anche se non con sicurezza, onde di gravità con periodo rispettivamente di circa 100 min e di 2 ore. In agosto la perita di energia per unità di massa delle onde interne di gravità assume nella regione tra 80 e 100 km valori compresi tra 0.015 e 0.045 W kg⁻¹ e la quantità di moto trasferita da queste onde a 90 km è 2.4 m s⁻¹ per ora. In particolari condizioni le accelerazioni del vento prevalente ((3÷4) m s⁻¹ al giorno) osservate in seguito al trasferimento delle quantità di moto in un periodo di 4 giorni consecutivi (24–27 agosto) possono essere compatibili con il valore elevato calcolato in precedenza.

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Резюме Проведены измерения ветров с помощью CNR радарной станции атмосферных явлений в Будрио (45° N, 12° E) в период с апреля по сентябрь 1978, обращая особое внимание на роль внутренних гравитационных волн в нижней термосфере ((80÷110) км). После краткого описания основных свойств этих волн мы определяем некоторые характеристики этих волн, используя обычные методы спектрального анализа и для кратковременной последовательности данных метод максимальной энтропии. Фурье-анализ этих данных показывает что гравитационные волны с периодами 2<T<8 часов имеют амплитуды, увеличивающиеся с высотой (вплоть до (30÷40) мс⁻¹ на высоте 100 км, в июне), вертикальные длины волн (8÷40) км и горизонтальные длины волн, превьшающие соответствующие значения вертикальных в 50 или более раз. В мае и сентябре, используя метод максимальной энтропии с выборкой (10÷20) минут, были предварительно индентифицированы гравитационные волны с периодами соответственно около 100 минут и 2 часов. В августе интенсивность энергетических потерь на единицу массы для внутренних гравитационных волн составляла от 0.015 до 0.045 Вт кг⁻¹ в области (80÷100) км и ослабление импульса этих волн составляет 2.4 мс⁻¹ час⁻¹ на высоте 90 км. При некоторых специаляных условиях наблюденных ускорения преобладающих ветров ((3÷4) мс⁻¹ день⁻¹), из-за ослабления импулчса, в течение 4 последовательных дней (24–27 августа) могут достигать вышеуказанного максимального значения.

     

Thin liquid layers in shear: non-Newtonian effects

When shear flow is generated in molecularly thin liquid films of simple liquids confined between two parallel plates, the effective viscosity of the liquid increases by many orders of magnitude compared to its bulk value. Non-Newtonian effects such as shear thinning with a universal power law exponent of are observed in experiments and computer simulations. We present a simple model of these phenomena based on shear melting of solid-like layers induced by the strong coupling with the crystalline walls.     

Direct numerical experiment on the measurement of the dispersion relation for gravity waves in the presence of the condensate

During previous numerical experiments on isotropic turbulence of surface gravity waves we observed formation of the long wave background (condensate). It was shown (Korotkevich, Phys. Rev. Lett. 101, 074504 (2008)) that the presence of the condensate changes a spectrum of direct cascade, corresponding to the flux of energy to the small scales from pumping region (large scales). Recent experiments show that the inverse cascade spectrum is also affected by the condensate. In this case mechanism proposed as a cause for the change of direct cascade spectrum cannot work. But inverse cascade is directly influenced by the linear dispersion relation for waves, as a result direct measurement of the dispersion relation in the presence of condensate is necessary. We performed the measurement of this dispersion relation from the direct numerical experiment. The results demonstrate that in the region of inverse cascade influence of the condensate cannot be neglected.     

Stochastic equations for gravity

The Langevin equations governing stochastic quantization of gravity are established. These equations hold true, independently of the value of the torsion. They are covariant under the BRS symmetry associated to local diffeomorphisms and Lorentz transformations. The method determines simultaneously the Langevin equations of the diffeomorphisms and Lorentz ghosts, and of the classical vielbein and spin connection.