44,074 research outputs found
Single wall penetration equations
Five single plate penetration equations are compared for accuracy and effectiveness. These five equations are two well-known equations (Fish-Summers and Schmidt-Holsapple), two equations developed by the Apollo project (Rockwell and Johnson Space Center (JSC), and one recently revised from JSC (Cour-Palais). They were derived from test results, with velocities ranging up to 8 km/s. Microsoft Excel software was used to construct a spreadsheet to calculate the diameters and masses of projectiles for various velocities, varying the material properties of both projectile and target for the five single plate penetration equations. The results were plotted on diameter versus velocity graphs for ballistic and spallation limits using Cricket Graph software, for velocities ranging from 2 to 15 km/s defined for the orbital debris. First, these equations were compared to each other, then each equation was compared with various aluminum projectile densities. Finally, these equations were compared with test results performed at JSC for the Marshall Space Flight Center. These equations predict a wide variety of projectile diameters at a given velocity. Thus, it is very difficult to choose the 'right' prediction equation. The thickness of a single plate could have a large variation by choosing a different penetration equation. Even though all five equations are empirically developed with various materials, especially for aluminum alloys, one cannot be confident in the shield design with the predictions obtained by the penetration equations without verifying by tests
Plant root proliferation in nitrogen-rich patches confers competitive advantage
Plants respond to environmental heterogeneity, particularly below ground, where spectacular root proliferations in nutrient-rich patches may occur. Such 'foraging' responses apparently maximize nutrient uptake and are now prominent in plant ecological theory. Proliferations in nitrogen-rich patches are difficult to explain adaptively, however. The high mobility of soil nitrate should limit the contribution of proliferation to N capture. Many experiments on isolated plants show only a weak relation between proliferation and N uptake. We show that N capture is associated strongly with proliferation during interspecific competition for finite, locally available, mixed N sources, precisely the conditions under which N becomes available to plants on generally infertile soils. This explains why N-induced root proliferation is an important resource-capture mechanism in N-limited plant communities and suggests that increasing proliferation by crop breeding or genetic manipulation will have a limited impact on N capture by well-fertilized monocultures
Lucy : Dancing Around The Cabin Door
https://digitalcommons.library.umaine.edu/mmb-vp/5190/thumbnail.jp
Heun equation, Teukolsky equation, and type-D metrics
Starting with the whole class of type-D vacuum backgrounds with cosmological
constant we show that the separated Teukolsky equation for zero rest-mass
fields with spin (gravitational waves), (electromagnetic
waves) and (neutrinos) is an Heun equation in disguise.Comment: 27 pages, corrected typo in eq. (1
Object orientation without extending Z
The good news of this paper is that without extending Z,
we can elegantly specify object-oriented systems, including encapsulation,
inheritance and subtype polymorphism (dynamic dispatch). The
bad news is that this specification style is rather different to normal
Z specifications, more abstract and axiomatic, which means that it is
not so well supported by current Z tools such as animators. It also enforces
behavioural subtyping, unlike most object-oriented programming
languages. This paper explains the proposed style, with examples, and
discusses its advantages and disadvantages
The impact of infrastructure investment on economic growth in the United Kingdom
ABSTRACT
Infrastructure investment has long been held as an accelerator or a driver of the economy. Internationally, the UK ranks poorly with the performance of infrastructure and ranks in the lower percentile for both infrastructure investment and GDP growth rate amongst comparative nations. Faced with the uncertainty of Brexit and the likely negative economic impact this will bring, infrastructure investment may be used to strengthen the UK economy. This study aims to examine how infrastructure funding impacts economic growth and how best the UK can maximize this potential by building on existing work.
The research method is based on interviews carried out with respondents involved in infrastructure operating across various sectors. The findings show that investment in infrastructure is vital in the UK as it stimulates economic growth through employment creation due to factor productivity. However, it is critical for investment to be directed to regional opportunity areas with the potential to unlock economic growth and maximize returns whilst stimulating further growth to benefit other regions. There is also a need for policy consistency and to review UK infrastructure policy to streamline the process and to reduce cost and time overrun, with Brexit likely to impact negatively on infrastructure investment. Keywords: infrastructure; economic growth; investment; constructio
Some Physical Consequences of Abrupt Changes in the Multipole Moments of a Gravitating Body
The Barrab\`es-Israel theory of light-like shells in General Relativity is
used to show explicitly that in general a light-like shell is accompanied by an
impulsive gravitational wave. The gravitational wave is identified by its
Petrov Type N contribution to a Dirac delta-function term in the Weyl conformal
curvature tensor (with the delta-function singular on the null hypersurface
history of the wave and shell). An example is described in which an
asymptotically flat static vacuum Weyl space-time experiences a sudden change
across a null hypersurface in the multipole moments of its isolated axially
symmetric source. A light-like shell and an impulsive gravitational wave are
identified, both having the null hypersurface as history. The stress-energy in
the shell is dominated (at large distance from the source) by the jump in the
monopole moment (the mass) of the source with the jump in the quadrupole moment
mainly responsible for the stress being anisotropic. The gravitational wave
owes its existence principally to the jump in the quadrupole moment of the
source confirming what would be expected.Comment: 26 pages, tex, no figures, to appear in Phys.Rev.
Children's suggestibility in relation to their understanding about sources of knowledge
In the experiments reported here, children chose either to maintain their initial belief about an object's identity or to accept the experimenter's contradicting suggestion. Both 3â to 4âyearâolds and 4â to 5âyearâolds were good at accepting the suggestion only when the experimenter was better informed than they were (implicit source monitoring). They were less accurate at recalling both their own and the experimenter's information access (explicit recall of experience), though they performed well above chance. Children were least accurate at reporting whether their final belief was based on what they were told or on what they experienced directly (explicit source monitoring). Contrasting results emerged when children decided between contradictory suggestions from two differentially informed adults: Threeâ to 4âyearâolds were more accurate at reporting the knowledge source of the adult they believed than at deciding which suggestion was reliable. Decision making in this observation task may require reflective understanding akin to that required for explicit source judgments when the child participates in the task
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