4,178 research outputs found
Rotorcraft convertible engine study
The objective of the Rotorcraft Convertible Engine Study was to define future research and technology effort required for commercial development by 1988 of convertible fan/shaft gas turbine engines for unconventional rotorcraft transports. Two rotorcraft and their respective missions were defined: a Fold Tilt Rotor aircraft and an Advancing Blade Concept (ABC) rotorcraft. Sensitivity studies were conducted with these rotorcraft to determine parametrically the influence of propulsion characteristics on aircraft size, mission fuel requirements, and direct operating costs (DOC). The two rotorcraft were flown with conventional propulsion systems (separate lift/cruise engines) and with convertible propulsion systems to determine the benefits to be derived from convertible engines. Trade-off studies were conducted to determine the optimum engine cycle and staging arrangement for a convertible engine. Advanced technology options applicable to convertible engines were studied. Research and technology programs were identified which would ensure technology readiness for commercial development of convertible engines by 1988
A recollimation shock 80 mas from the core in the jet of the radio galaxy 3C120: Observational evidence and modeling
We present Very Long Baseline Array observations of the radio galaxy 3C120 at
5, 8, 12, and 15 GHz designed to study a peculiar stationary jet feature
(hereafter C80) located ~80 mas from the core, which was previously shown to
display a brightness temperature ~600 times lager than expected at such
distances. The high sensitivity of the images -- obtained between December 2009
and June 2010 -- has revealed that C80 corresponds to the eastern flux density
peak of an arc of emission (hereafter A80), downstream of which extends a large
(~20 mas in size) bubble-like structure that resembles an inverted bow shock.
The linearly polarized emission closely follows that of the total intensity in
A80, with the electric vector position angle distributed nearly perpendicular
to the arc-shaped structure. Despite the stationary nature of C80/A80,
superluminal components with speeds up to ~3 c have been detected downstream
from its position, resembling the behavior observed in the HST-1 emission
complex in M87. The total and polarized emission of the C80/A80 structure, its
lack of motion, and brightness temperature excess are best reproduced by a
model based on synchrotron emission from a conical shock with cone opening
angle \eta=10 degrees, jet viewing angle \theta=16 degrees, a completely
tangled upstream magnetic field, and upstream Lorentz factor \gamma=8.4. The
good agreement between our observations and numerical modeling leads us to
conclude that the peculiar feature associated with C80/A80 corresponds to a
conical recollimation shock in the jet of 3C120 located at a de-projected
distance of ~190 pc downstream from the nucleus.Comment: Accepted for publication in Ap
Follow your nose: chemical communication throughout the European eel (Anguilla anguilla, L.) life-cycle
European eels are important in both scientific and economic terms. Unfortunately, current populations are becoming increasingly endangered and urgentmanagement is needed. Several aspects of eel biology, together with their highly developed sense of smell, suggest
that chemical communication could be involved at key stages of their life-history. Thus, advances in this area could generate novel tools for stock management
Non-thermal moduli production during preheating in -attractor inflation models
Production of gravitationally coupled light moduli fields must be suppressed
in the early universe, so that its decay products do not alter Big Bang
Nucleosynthesis (BBN) predictions for light elements. On the other hand, the
moduli quanta can be copiously produced non-thermally during preheating after
the end of inflation. In this work, we study the production of moduli in the
-attractor inflationary model through parametric resonances. For our
case, where the inflationary potential at its minimum is quartic, the inflaton
field self-resonates, and subsequently induces large production of moduli
particles. We find that this production is suppressed for small values of
. Combining semi-analytical estimation and numerical lattice
simulations, we infer the parametric dependence on and learn that
needs to be to be consistent with
BBN. This in turn predicts an upper bound on the energy scale of inflation and
on the reheating temperature.Comment: v1: 24 pages, 8 figures; v2: 30 pages, 11 figures, added two
appendices, updated discussions and references, matches published versio
Changes in ageâstructure over four decades were a key determinant of population growth rate in a longâlived mammal
1. A changing environment directly influences birth and mortality rates, and thus population growth rates. However, population growth rates in the short term are also influenced by population ageâstructure. Despite its importance, the contribution of ageâstructure to population growth rates has rarely been explored empirically in wildlife populations with longâterm demographic data.
2. Here we assessed how changes in ageâstructure influenced shortâterm population dynamics in a semiâcaptive population of Asian elephants Elephas maximus .
3. We addressed this question using a demographic dataset of female Asian elephants from timber camps in Myanmar spanning 45 years (1970â2014). First, we explored temporal variation in ageâstructure. Then, using annual matrix population models, we used a retrospective approach to assess the contributions of ageâstructure and vital rates to shortâterm population growth rates with respect to the average environment.
4. Ageâstructure was highly variable over the study period, with large proportions of juveniles in the years 1970 and 1985, and made a substantial contribution to annual population growth rate deviations. High adult birth rates between 1970 and 1980 would have resulted in large positive population growth rates, but these were prevented by a low proportion of reproductiveâaged females.
5. We highlight that an understanding of both ageâspecific vital rates and ageâstructure is needed to assess shortâterm population dynamics. Furthermore, this example from a humanâmanaged system suggests that the importance of ageâstructure may be accentuated in populations experiencing human disturbance where ageâstructure is unstable, such as those in captivity or for endangered species. Ultimately, changes to the environment drive population dynamics by influencing birth and mortality rates, but understanding demographic structure is crucial for assessing population growth
Palatini versus metric formulation in higher curvature gravity
We compare the metric and the Palatini formalism to obtain the Einstein
equations in the presence of higher-order curvature corrections that consist of
contractions of the Riemann tensor, but not of its derivatives. We find that
there is a class of theories for which the two formalisms are equivalent. This
class contains the Palatini version of Lovelock theory, but also more
Lagrangians that are not Lovelock, but respect certain symmetries. For the
general case, we find that imposing the Levi-Civita connection as an Ansatz,
the Palatini formalism is contained within the metric formalism, in the sense
that any solution of the former also appears as a solution of the latter, but
not necessarily the other way around. Finally we give the conditions the
solutions of the metric equations should satisfy in order to solve the Palatini
equations.Comment: 13 pages, latex. V2: reference added, major changes in section 3,
conclusions partially correcte
Identification of a Profile of Neutrophil-Derived Granule Proteins in the Surface of Gold Nanoparticles after Their Interaction with Human Breast Cancer Sera
It is well known that the interaction of a nanomaterial with a biological fluid leads to the formation of a protein corona (PC) surrounding the nanomaterial. Using standard blood analyses, alterations in protein patterns are difficult to detect. PC acts as a "nano-concentrator" of serum proteins with affinity for nanoparticles' surface. Consequently, characterization of PC could allow detection of otherwise undetectable changes in protein concentration at an early stage of a disease, such as breast cancer (BC). Here, we employed gold nanoparticles (AuNPsdiameter: 10.02 +/- 0.91 nm) as an enrichment platform to analyze the human serum proteome of BC patients (n = 42) and healthy controls (n = 42). Importantly, the analysis of the PC formed around AuNPs after their interaction with serum samples of BC patients showed a profile of proteins that could differentiate breast cancer patients from healthy controls. These proteins developed a significant role in the immune and/or innate immune system, some of them being neutrophil-derived granule proteins. The analysis of the PC also revealed serum proteome alterations at the subtype level
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