The First Eocene Rodents From the Pacific Northwest, USA

The Oligocene and Miocene faunas of the John Day Basin are diverse and very well-studied, including a large number of small mammal species. Though Eocene floras from Oregon are well-known, Eocene faunas include relatively few taxa from only two described localities in the Clarno area. The first Eocene rodents from the John Day Basin also include the first ischyromyids from the Pacific Northwest. Several rodent incisors were recovered from the Hancock Mammal Quarry at Clarno, representing the first rodent specimens known from the Clarno Formation. The Hancock Mammal Quarry lies between tuffs dated 42.7 and 39.22 Ma, meaning these rodents are latest Uintan or earliest Duchesnean in age. Several ischyromyids are also described from the Big Basin Member of the John Day Formation. From a Duchesnean locality between tuffs dated 39.22 and 38.4 Ma a single tooth of Pseudotomus was recovered, which is as large as any known ischyromyid. Another Big Basin Member site yielded a new genus and species of ischyromyid. That site lies above an ash dated 36.21 Ma and biostratigraphy confirms a Chadronian age. These rodents help fill important gaps in the fossil record of the John Day Basin and will facilitate comparisons with other Eocene sites in North America and Asia

Evolution in Yoderimyinae (Eomyidae: Rodentia), with new material from the White River Formation (Chadronian) at Flagstaff Rim, Wyoming

Three species of Yoderimyinae (Eomyidae: Rodentia) are recognized from the lower part of the White River Formation (early to medial Chadronian) in the Flagstaff Rim area, Wyoming. The new material allows an improved diagnosis for the subfamily. The enamel microstructure of Yoderimyinae supports its inclusion in the Eomyidae. A new genus, Zemiodontomys, is established for Yoderimys burkei Black, and new material, including upper dentition, is referred to this species. This genus differs from Yoderimys in having higher crowned and more lophodont teeth and in lacking P3. A second new genus, Litoyoderimys, is established for Yoderimys lustrorum Wood, and a new species, L. auogoleus, is referred to the genus. This genus has lower crowned, more cuspate teeth than Yoderimys. Through early and medial Chadronian time, evolution in yoderimyines includes the following morphologic transformations: increase in size; increase in crown height and lophodonty of cheek teeth; reduction of P3 (from double-rooted, to single-rooted, to absent); increase in relative size of P4 and p4; and increased longitudinal torsion of the mandibl

Narrowing the filter cavity bandwidth via optomechanical interaction

We propose using optomechanical interaction to narrow the bandwidth of filter cavities for achieving frequency-dependent squeezing in advanced gravitational-wave detectors, inspired by the idea of optomechanically induced transparency. This not only allows us to achieve narrow bandwidth, comparable to the detection band of few hundred Hz, with tabletop optical cavities, but also to tune the bandwidth over a wide range, which is ideal for optimizing sensitivity for different gravitational-wave sources. The experimental challenge for its implementation is the stringent requirement on low thermal noise, which would need superb mechanical quality factor that is quite difficult to achieve by using currently-available low-loss mechanical oscillators; one possible solution is to use optical dilution of the mechanical damping, which can considerably relax the requirement on the mechanics.Comment: 5 pages + 3 appendix. 4 figures and 2 tables Accepted by Physical Review Letter

Narrowing the Filter-Cavity Bandwidth in Gravitational-Wave Detectors via Optomechanical Interaction

We propose using optomechanical interaction to narrow the bandwidth of filter cavities for achieving frequency-dependent squeezing in advanced gravitational-wave detectors, inspired by the idea of optomechanically induced transparency. This can allow us to achieve a cavity bandwidth on the order of 100 Hz using small-scale cavities. Additionally, in contrast to a passive Fabry-Pérot cavity, the resulting cavity bandwidth can be dynamically tuned, which is useful for adaptively optimizing the detector sensitivity when switching amongst different operational modes. The experimental challenge for its implementation is a stringent requirement for very low thermal noise of the mechanical oscillator, which would need a superb mechanical quality factor and a very low temperature. We consider one possible setup to relieve this requirement by using optical dilution to enhance the mechanical quality factor

The initial temporal evolution of a feedback dynamo for Mercury

Various possibilities are currently under discussion to explain the observed weakness of the intrinsic magnetic field of planet Mercury. One of the possible dynamo scenarios is a dynamo with feedback from the magnetosphere. Due to its weak magnetic field Mercury exhibits a small magnetosphere whose subsolar magnetopause distance is only about 1.7 Hermean radii. We consider the magnetic field due to magnetopause currents in the dynamo region. Since the external field of magnetospheric origin is antiparallel to the dipole component of the dynamo field, a negative feedback results. For an alpha-omega-dynamo two stationary solutions of such a feedback dynamo emerge, one with a weak and the other with a strong magnetic field. The question, however, is how these solutions can be realized. To address this problem, we discuss various scenarios for a simple dynamo model and the conditions under which a steady weak magnetic field can be reached. We find that the feedback mechanism quenches the overall field to a low value of about 100 to 150 nT if the dynamo is not driven too strongly

The composition of heavy molecular ions inside the ionopause of Comet Halley

The RPA2-PICCA instrument aboard the Giotto spacecraft obtained 10-210 amu mass spectral of cold thermal molecular ions in the coma of Comet Halley. The dissociation products of the long chain formaldehyde polymer polyoxymethylene (POM) have recently been proposed as the dominant complex molecules in the coma of Comet Halley; however, POM alone cannot account for all of the features of the high resolution spectrum. An important component of the dust at Comet Halley is particles highly enriched in carbon, hydrogen, oxygen, and nitrogen relative to the composition of carbonaceous chondrites. Since this dust could be a source for the heavy molecules observed by PICCA, a search was conducted for other chemical species by determining all the molecules with mass between 20 and 120 amu which can be made from the relatively abundant C, H, O, and N, without regard to chemical structure

Suppression of quantum-radiation-pressure noise in an optical spring

Recent advances in micro- and nanofabrication techniques have led to corresponding improvement in the performance of optomechanical systems, which provide a promising avenue towards quantum-limited metrology and the study of quantum behavior in macroscopic mechanical objects. One major impediment to reaching the quantum regime is thermal excitation, which can be overcome for a sufficiently high mechanical quality factor Q. Here, we propose a method for increasing the effective Q of a mechanical resonator by stiffening it via the optical spring effect exhibited by linear optomechanical systems and show how the associated quantum-radiation-pressure noise can be evaded by sensing and feedback control. In a parameter regime that is attainable with current technology, this method allows for realistic quantum cavity optomechanics in a frequency band well below that which has been realized thus far

Passive, free-space heterodyne laser gyroscope

Laser gyroscopes making use of the Sagnac effect have been used as highly accurate rotation sensors for many years. First used in aerospace and defense applications, these devices have more recently been used for precision seismology and in other research settings. In particular, mid-sized (~1 m-scale) laser gyros have been under development as tilt sensors to augment the adaptive active seismic isolation systems in terrestrial interferometric gravitational wave detectors. The most prevalent design is the 'active' gyroscope, in which the optical ring cavity used to measure the Sagnac degeneracy breaking is itself a laser resonator. In this article, we describe another topology: a 'passive' gyroscope, in which the sensing cavity is not itself a laser but is instead tracked using external laser beams. While subject to its own limitations, this design is free from the deleterious lock-in effects observed in active systems, and has the advantage that it can be constructed using commercially available components. We demonstrate that our device achieves comparable sensitivity to those of similarly sized active laser gyroscopes

Multi-color Cavity Metrology

Long baseline laser interferometers used for gravitational wave detection have proven to be very complicated to control. In order to have sufficient sensitivity to astrophysical gravitational waves, a set of multiple coupled optical cavities comprising the interferometer must be brought into resonance with the laser field. A set of multi-input, multi-output servos then lock these cavities into place via feedback control. This procedure, known as lock acquisition, has proven to be a vexing problem and has reduced greatly the reliability and duty factor of the past generation of laser interferometers. In this article, we describe a technique for bringing the interferometer from an uncontrolled state into resonance by using harmonically related external fields to provide a deterministic hierarchical control. This technique reduces the effect of the external seismic disturbances by four orders of magnitude and promises to greatly enhance the stability and reliability of the current generation of gravitational wave detector. The possibility for using multi-color techniques to overcome current quantum and thermal noise limits is also discussed