Parallax of Star-forming Region G027.22+0.14

Using the Very Long Baseline Array, we measured the trigonometric parallax and proper motions toward a 6.7 GHz methanol maser in the distant high-mass star-forming region G027.22+0.14. The distance of this source is determined to be 6.3 − 0.5 + 0.6 kpc. Combining its Galactic coordinates, radial velocity, and proper motion, we assign G027.22+0.14 to the far portion of the Norma arm. The low peculiar motion and lower luminosity of G027.22+0.14 support the conjecture by Immer et al. that low-luminosity sources tend to have low peculiar motions.

The Kaiser-Rocket effect: three decades and counting

The peculiar motion of the observer, if not accurately accounted for, is bound to induce a well-defined clustering signal in the distribution of galaxies. This signal is related to the Kaiser rocket effect. Here we examine the amplitude and form of this effect, both analytically and numerically, and discuss possible implications for the analysis and interpretation of forthcoming cosmological surveys. For an idealistic cosmic variance dominated full-sky survey with a Gaussian selection function peaked at z ∼ 1.5 it is a > 5σ effect and it can in principle bias very significantly the inference of cosmological parameters, especially for primordial non-Gaussianity. For forthcoming surveys, with realistic masks and selection functions, the Kaiser rocket is not a significant concern for cosmological parameter inference except perhaps for primordial non-Gaussianity studies. However, it is a systematic effect, whose origin, nature and imprint on galaxy maps are well known and thus should be subtracted or mitigated. We present several approaches to do so.

On the connection between cosmological parameters and peculiar motion in a G2 massless scalar field spacetime

The geodesic motion of a massive test particle in a [Formula: see text] massless scalar field universe is investigated. The time evolution of the peculiar velocity is connected to the values of the cosmological parameters, and it is quantified how the spacetime shearing effects affect the deviations from the asymptotic value of comoving matter flow at late epochs. On the other hand, it is shown that the energy scale of the cosmic fluid does not affect the evolution of the peculiar velocity. The existence of a turning point in the motion of the astronomical object is identified. The potential astrophysical relevance of this study in the modeling of cosmic filaments and Large Quasar Groups is briefly discussed.

The peculiar Jeans length

Typical observers in the universe do not follow the smooth Hubble expansion, but move relative to it. Such bulk peculiar motions introduce a characteristic scale that is closely analogous to the familiar Jeans length. This “peculiar Jeans length” marks the threshold below which relative-motion effects dominate the linear kinematics. There, cosmological measurements can vary considerably between the bulk-flow frame and that of the Hubble expansion, entirely due to the observers’ relative motion. When dealing with the deceleration parameter, we find that the peculiar Jeans length varies between few and several hundred Mpc. On these scales, the deceleration parameter measured by the bulk-flow observers can be considerably larger (or smaller) than its Hubble-frame counterpart. This depends on whether the peculiar motion is locally expanding (or contracting), relative to the background expansion. Then, provided expanding and contracting bulk flows are randomly distributed, nearly half of the observers in the universe could be misled to think that their cosmos is over-decelerated. The rest of them, on the other hand, may come to believe that their universe is under-decelerated, or even accelerated in some cases. We make two phenomenological predictions that could in principle support this scenario.

Our Peculiar Motion Inferred from Number Counts of Mid Infra Red AGNs and the Discordance Seen with the Cosmological Principle

According to the Cosmological Principle, the Universe is isotropic and no preferred direction would be seen by an observer that might be stationary with respect to the expanding cosmic fluid. However, because of observer’s partaking in the solar system peculiar motion, there would appear in some of the observed properties of the Cosmos a dipole anisotropy, which could in turn be exploited to determine the peculiar motion of the solar system. The dipole anisotropy in the Cosmic Microwave Background Radiation (CMBR) has given a peculiar velocity vector 370 km s−1 along l=264∘,b=48∘. However, some other dipoles, for instance, from the number counts, sky brightness or redshift distributions in large samples of distant Active Galactic Nuclei (AGNs), have yielded values of the peculiar velocity many times larger than that from the CMBR, though surprisingly, in all cases the directions agreed with the CMBR dipole. Here we determine our peculiar motion from a sample of 0.28 million AGNs, selected from the Mid Infra Red Active Galactic Nuclei (MIRAGN) sample comprising more than a million sources. From this, we find a peculiar velocity, which is more than four times the CMBR value, although the direction seems to be within ∼2σ of the CMBR dipole. A genuine value of the solar peculiar velocity should be the same irrespective of the data or the technique employed to estimate it. Therefore, such discordant dipole amplitudes might mean that the explanation for these dipoles, including that of the CMBR, might in fact be something else. The observed fact that the direction in all cases is the same, though obtained from completely independent surveys using different instruments and techniques, by different sets of people employing different computing routines, might nonetheless indicate that these dipoles are not merely due to some systematics, otherwise why would they all be pointing along the same direction. It might instead suggest a preferred direction in the Universe, implying a genuine anisotropy, which would violate the Cosmological Principle, the core of the modern cosmology.

Analysis of a Wearable Robotic System for Ankle Rehabilitation

As one of the most commonly injured joints of the human body, the ankle is often subject to sprains or fractures that require motion assistance to recover mobility. Whereas physiotherapists usually perform rehabilitation in one-on-one sessions with patients, several successful robotic rehabilitation solutions have been proposed in the last years. However, their design is usually bulky and requires the patient to sit or stand in a static position. A lightweight wearable device for ankle motion assistance, the CABLEankle, is here proposed for motion ankle exercising in rehabilitation and training. The CABLEankle is based on a cable-driven S-4SPS parallel architecture, which enables motion assistance over the large motion range of the human ankle in a walking gait. The proposed mechanism design is analyzed with kinematic and static models, and the force closure workspace of the mechanism is discussed with analytical results. Finally, the feasibility of the proposed design is investigated through numerical simulations over the ankle motion range as a characterization of the peculiar motion.

Redshifting Cosmic Photons in a Non-Expanding Universe

Cosmologists present clear observational evidences that stellar objects like stars and galaxies do carry out pronounced proper motions, and the question may be raising how these peculiar motions might evolve in time. In this article we study these peculiar motions of single objects, independent whether of microscopic or macroscopic nature, embedded in a globally homogeneous, static, massive universe with inherent gravity. Aims: We show that these objects at their motions, even in a homogeneous universe around them, are permanently subject to net gravitational forces due to the fact that in a post-Newtonian relativistic treatment the sources of cosmic masses are seen under retarded positions, retarded by the time it takes to communicate via gravitons the positions of these masses to the moving object. Methods: This “aberrational” recognition of massive source points on the one hand leads to a braking power permanently decelerating the peculiar motion of any cosmic object, on the other hand it also effects the wave lengths of all photons freely propagating through cosmic space under the action of cosmic gravity. Photons, even in a static homogeneous universe, undergo a permanent red-shifting, since working permanently against a net gravitational force from the direction opposite to the photon’s propagation direction. Results: We do show that the observationally confirmed redshifts of photons from distant galaxies under the new auspices appear as a pure measure of the distance which the photons passed from its galactic emitter to us. In this view redshifts have nothing to do with the Hubble dynamics of the universe and its emitters. Since, however, the existence of Hubble-induced redshifts cannot be excluded, we also look into a combination of both, gravitationally induced redshifts zg and Hubble-induced redshifts zH. We show that gravitationally induced redshifts zg of course also appear in an expanding universe, and it can be demonstrated that for instance in a “coasting universe” with a constant expansion rate R˙ and with R α t both these redshifts zg and zH would lead to similar results.