273 research outputs found
New Methods of Manufacturing Space Suits for Deep Space Exploration
The Extravehicular Activity (EVA) spacesuit is a complex machine that provides astronauts with a flexible enclosure and life support system allowing them to perform EVAs in space or on planetary surfaces. As humans continue to explore the Solar System, the ability for space fairing organizations to become Earth-autonomous is a necessity, and the need for an Earth-independent spacesuit is unavoidable. With the evolution of additive manufacturing technologies, it may be possible to produce 3D-printed soft goods that can replace the labor-intensive bladders and restraint layers currently in pressure suits. The Human Spaceflight Laboratory (HSFL) at the University of North Dakota has demonstrated the ability to use additive manufacturing to develop various soft spacesuit components. By utilizing flexible filaments in combination with interwoven mesh fabrics for improved durability, the HSFL has been able to produce various soft goods components, a functional elbow mobility joint and a boot/ankle assembly. The components have been successfully tested at nominal spacesuit pressures along with burst tests at higher pressures. Through development and testing of these early prototypes, the HSFL has proved that additive manufacturing can be utilized to fabricate spacesuit elements. The HSFL plans to build upon the advancements discussed in this paper and continue to employ additive manufacturing techniques with the end goal of developing a fully functional 3D-printed pressure garment based on our existing NDX-1 planetary suit architecture
Latent solitons, black strings, black branes, and equations of state in Kaluza-Klein models
In Kaluza-Klein models with an arbitrary number of toroidal internal spaces,
we investigate soliton solutions which describe the gravitational field of a
massive compact object. We single out the physically interesting solution
corresponding to a point-like mass. For the general solution we obtain
equations of state in the external and internal spaces. These equations
demonstrate that the point-like mass soliton has dust-like equations of state
in all spaces. We also obtain the PPN parameters, which give the possibility to
obtain the formulas for perihelion shift, deflection of light and time delay of
radar echoes. Additionally, the gravitational experiments lead to a strong
restriction on the parameter of the model: . The point-like mass solution contradicts this restriction. The
condition satisfies the experimental limitation and defines a new
class of solutions which are indistinguishable from general relativity. We call
such solutions latent solitons. Black strings and black branes belong to this
class. Moreover, the condition of stability of the internal spaces singles out
black strings/branes from the latent solitons and leads uniquely to the black
string/brane equations of state , in the internal spaces and
to the number of the external dimensions . The investigation of
multidimensional static spherically symmetric perfect fluid with dust-like
equation of state in the external space confirms the above results.Comment: 8 pages, Revtex4, no figures, minor changes adde
Kaluza-Klein models: can we construct a viable example?
In Kaluza-Klein models, we investigate soliton solutions of Einstein
equation. We obtain the formulas for perihelion shift, deflection of light,
time delay of radar echoes and PPN parameters. We find that the solitonic
parameter k should be very big: |k|\geq 2.3\times10^4. We define a soliton
solution which corresponds to a point-like mass source. In this case the
soliton parameter k=2, which is clearly contrary to this restriction. Similar
problem with the observations takes place for static spherically symmetric
perfect fluid with the dust-like equation of state in all dimensions. The
common for both of these models is the same equations of state in our three
dimensions and in the extra dimensions. All dimensions are treated at equal
footing. To be in agreement with observations, it is necessary to break the
symmetry between the external/our and internal spaces. It takes place for black
strings which are particular examples of solitons with k\to \infty. For such k,
black strings are in concordance with the observations. Moreover, we show that
they are the only solitons which are at the same level of agreement with the
observations as in general relativity. Black strings can be treated as perfect
fluid with dust-like equation of state p_0=0 in the external/our space and very
specific equation of state p_1=-(1/2)\epsilon in the internal space. The latter
equation is due to negative tension in the extra dimension. We also demonstrate
that dimension 3 for the external space is a special one. Only in this case we
get the latter equation of state. We show that the black string equations of
state satisfy the necessary condition of the internal space stabilization.
Therefore, black strings are good candidates for a viable model of
astrophysical objects (e.g., Sun) if we can provide a satisfactory explanation
of negative tension for particles constituting these objects.Comment: 11 pages, Revtex4, no figures, appendix and references adde
Lorentz violation and the speed of gravitational waves in brane-worlds
Lorentz violation in a brane-world scenario is presented and used to obtain a
relationship between the speed of gravitational waves in the bulk and that on
the brane. Lorentz violating effects would manifest themselves in gravitational
waves travelling with a greater speed in the bulk than on the brane and this
effect is independent of the signature of the extra dimension.Comment: 8 pages, to appear in PL
Static wormholes on the brane inspired by Kaluza-Klein gravity
We use static solutions of 5-dimensional Kaluza-Klein gravity to generate
several classes of static, spherically symmetric spacetimes which are analytic
solutions to the equation , where is the
four-dimensional Ricci scalar. In the Randall & Sundrum scenario they can be
interpreted as vacuum solutions on the brane. The solutions contain the
Schwarzschild black hole, and generate new families of traversable Lorenzian
wormholes as well as nakedly singular spacetimes. They generalize a number of
previously known solutions in the literature, e.g., the temporal and spatial
Schwarzschild solutions of braneworld theory as well as the class of self-dual
Lorenzian wormholes. A major departure of our solutions from Lorenzian
wormholes {\it a la} Morris and Thorne is that, for certain values of the
parameters of the solutions, they contain three spherical surfaces (instead of
one) which are extremal and have finite area. Two of them have the same size,
meet the "flare-out" requirements, and show the typical violation of the energy
conditions that characterizes a wormhole throat. The other extremal sphere is
"flaring-in" in the sense that its sectional area is a local maximum and the
weak, null and dominant energy conditions are satisfied in its neighborhood.
After bouncing back at this second surface a traveler crosses into another
space which is the double of the one she/he started in. Another interesting
feature is that the size of the throat can be less than the Schwarzschild
radius , which no longer defines the horizon, i.e., to a distant observer
a particle or light falling down crosses the Schwarzschild radius in a finite
time
Dynamics of Quintessence Models of Dark Energy with Exponential Coupling to the Dark Matter
We explore quintessence models of dark energy which exhibit non-minimal
coupling between the dark matter and the dark energy components of the cosmic
fluid. The kind of coupling chosen is inspired in scalar-tensor theories of
gravity. We impose a suitable dynamics of the expansion allowing to derive
exact Friedmann-Robertson-Walker solutions once the coupling function is given
as input. Self-interaction potentials of single and double exponential types
emerge as result of our choice of the coupling function. The stability and
existence of the solutions is discussed in some detail. Although, in general,
models with appropriated interaction between the components of the cosmic
mixture are useful to handle the coincidence problem, in the present study the
coincidence can not be evaded due to the choice of the solution generating
ansatz.Comment: 10 pages, 7 figure
Increasing Access to Food: A Comprehensive Report on Food Supply Options
Access to food is one of the most important aspects of a healthy, sustainable community. Grocery stores and other suppliers can serve as an economic anchor to provide social benefits to communities. Unfortunately, many communities do not have convenient and/or affordable access to grocery items, particularly fresh produce.
As part of Virginia Commonwealth University\u27s Fall 2019 graduate course on Urban Commercial Revitalization, class members researched 13 retail and other food access options, which are described in this report. Each chapter covers a food access option and provides basic information that will be useful to individuals, organizations, or government agencies that wish to attract and/or develop grocery operations in their communities
Design development of a repeatable helmet test system for public order threat recreations
The prevalence of violence and blunt weaponry that Public Order (PO) officers are exposed to, place them at high risk of traumatic brain injury (TBI). Recreating these injurious occurrences, to assess protective equipment performance, can be problematic due to issues of repeatability when experimentally recreating PO threats. This led to the design of a bespoke helmet impact system. Following review of current test methods, the chosen design was a low-friction drop tower, compatible with anthropometric headforms as cradled, rigidly mounted, or affixed with a surrogate neck. Finite Element and torque calculations were used to optimise load bearing components, whilst maintaining low mass and safety requirements. The final system permits impact conditions in range for PO threat recreations, as well as meeting the standard test criteria of all non-vehicular sports, public sector and construction application standard drop tests
Fierz-Pauli equation for massive gravitons from Induced Matter theory of gravity
Starting with a 5D physical vacuum described by a 5D Ricci-flat background
metric, we study the emergence of gravitational waves (GW) from the Induce
Matter (IM) theory of gravity. We obtain the equation of motion for GW on an 4D
curved spacetime which has the form of a Fierz-Pauli one. In our model the mass
of gravitons is induced by a static foliation on the noncompact
space-like extra dimension and the source-term is originated in the interaction
of the GW with the induced connections of the background 5D metric. Here,
relies the main difference of this formalism with the original Fierz-Pauli one.Comment: 9 pages, no figures, version accepted in Phys. Lett.
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