379 research outputs found
MASS TIMBER CONSTRUCTION IN AUSTRALIA AND NEW ZEALAND—STATUS, AND ECONOMIC AND ENVIRONMENTAL INFLUENCES ON ADOPTION
Mass timber construction in Australia and New Zealand uses three main materials—laminated veneer lumber, glue laminated timber and cross-laminated timber (CLT). This article focuses on the use of mass timber in nonresidential construction—the use in single-family homes and apartments is not considered. In Australia and New Zealand, mass timber building technology has moved from being technologically possible to being a feasible alternative to reinforced concrete and steel construction. It has not taken over a large market share in either market and, as such, has not been a disruptive technology. The major changes in this market in the past 5-10 yr in Australia and New Zealand have been the development of new industrial capacity in CLT and the acquisition of computer controlled machining equipment to facilitate prefabrication of wooden building components. The development of new codes and standards and design guides is underway. The drivers of future growth in market share are expected to include more clients putting a higher weight on the various environmental benefits of building in wood, reduction in the real and perceived professional risk for builders and architects specifying mass timber construction, and fuller participation in the supply chain for timber buildings (from design to construction) by timber building specialists. Government policies to encourage the use of timber may also be helpful. Engineers and architects will continue to learn—through experience—how to optimize building construction methods to take advantage of the specific features and qualities of timber as a construction method.Â
Filling the Knowledge Gaps in Mass Timber Construction: Where are the Missing Pieces, What are the Research Needs?
As mass timber construction evolves from a niche product to a mainstream, there is an urgent need for focused research activities to support the industry and avoid duplication or overlap of work being done internationally. To identify and prioritise the future of mass timber research agenda, this article pursues responses to the following questions: What is the current state of knowledge and where are the remaining research needs in mass timber construction? For example, newcomers to mass timber often believe it is imperative to research fire performance, fire resistance, or sound transmission when these areas have been extensively explored and are now widely seen as resolved. Consequently, the focus has shifted, towards answering new research questions, including explorations of carbon storage, and life cycle analysis durability. There is already a growing research activity in mass timber, involving several research centres worldwide, that would benefit from some guidance on research needs. Thus, defining new trends and research gaps that help avoid replicating research. A more nuanced discussion on knowledge gaps and industry research needs is also timely, to truly capture and disseminate information on the full potential of engineered-wood products as an innovative construction material, which helps reduce the use of carbon-intensive conventional building materials. To answer the above-mentioned research questions, this study has consulted experts at an international conference, and seven key research areas have been identified and presented as the results
The imprint of superradiance on hierarchical black hole mergers
Ultralight bosons are a proposed solution to outstanding problems in
cosmology and particle physics: they provide a dark-matter candidate while
potentially explaining the strong charge-parity problem. If they exist,
ultralight bosons can interact with black holes through the superradiant
instability. In this work we explore the consequences of this instability on
the evolution of hierarchical black holes within dense stellar clusters. By
reducing the spin of individual black holes, superradiance reduce the recoil
velocity of merging binary black holes, which, in turn, increases the retention
fraction of hierarchical merger remnants. We show that the existence of
ultralight bosons with mass would lead to an increased rate of hierarchical black
hole mergers in nuclear star clusters. An ultralight boson in this energy range
would result in up to more present-day nuclear star clusters
supporting hierarchical growth. The presence of an ultralight boson can also
double the rate of intermediate mass black hole mergers to
\,Gpc\,yr in the local Universe. These results imply
that a select range of ultralight boson mass can have far-reaching consequences
for the population of black holes in dense stellar environments. Future studies
into black hole cluster populations and the spin distribution of hierarchically
formed black holes will test this scenario.Comment: 20 pages, 7 figure
Gravitational Waves as a Probe of Globular Cluster Formation and Evolution
Globular clusters are considered to be likely breeding grounds for compact
binary mergers. In this paper, we demonstrate how the gravitational-wave
signals produced by compact object mergers can act as tracers of globular
cluster formation and evolution. Globular cluster formation is a long-standing
mystery in astrophysics, with multiple competing theories describing when and
how globular clusters formed. The limited sensitivity of electromagnetic
telescopes inhibits our ability to directly observe globular cluster formation.
However, with future audio-band detectors sensitive out to redshifts of for GW150914-like signals, gravitational-wave astronomy will enable
us to probe the Universe when the first globular clusters formed. We simulate a
population of binary black hole mergers from theoretically-motivated globular
cluster formation models, and construct redshift measurements consistent with
the predicted accuracy of third-generation detectors. We show that we can
locate the peak time of a cluster formation epoch during reionisation to within
0.05Gyr after one year of observations. The peak of a formation epoch that
coincides with the Universal star formation rate can be measured to within
0.4Gyr-10.5Gyr after one year of observations, depending on the relative
weighting of the model components
Tachyonization of the \LaCDM cosmological model
In this work a tachyonization of the CDM model for a spatially flat
Friedmann-Robertson-Walker space-time is proposed. A tachyon field and a
cosmological constant are considered as the sources of the gravitational field.
Starting from a stability analysis and from the exact solutions for a standard
tachyon field driven by a given potential, the search for a large set of
cosmological models which contain the CDM model is investigated. By
the use of internal transformations two new kinds of tachyon fields are derived
from the standard tachyon field, namely, a complementary and a phantom tachyon
fields. Numerical solutions for the three kinds of tachyon fields are
determined and it is shown that the standard and complementary tachyon fields
reproduces the CDM model as a limiting case. The standard tachyon
field can also describe a transition from an accelerated to a decelerated
regime, behaving as an inflaton field at early times and as a matter field at
late times. The complementary tachyon field always behaves as a matter field.
The phantom tachyon field is characterized by a rapid expansion where its
energy density increases with time.Comment: Version accepted for publication in GR
Heat Capacity of PbS: Isotope Effects
In recent years, the availability of highly pure stable isotopes has made
possible the investigation of the dependence of the physical properties of
crystals, in particular semiconductors, on their isotopic composition.
Following the investigation of the specific heat (, ) of monatomic
crystals such as diamond, silicon, and germanium, similar investigations have
been undertaken for the tetrahedral diatomic systems ZnO and GaN (wurtzite
structure), for which the effect of the mass of the cation differs from that of
the anion. In this article we present measurements for a semiconductor with
rock salt structure, namely lead sulfide. Because of the large difference in
the atomic mass of both constituents (= 207.21 and (=32.06 a.m.u., for the natural isotopic abundance) the effects of varying
the cation and that of the anion mass are very different for this canonical
semiconductor. We compare the measured temperature dependence of , and the corresponding derivatives with respect to ( and
), with \textit{\textit{ab initio}} calculations based on the
lattice dynamics obtained from the local density approximation (LDA) electronic
band structure. Quantitative deviations between theory and experiment are
attributed to the absence of spin-orbit interaction in the ABINIT program used
for the electronic band structure calculations.Comment: 17 pages including 10 Fig
Screening of Hydrodynamic Interactions in Semidilute Polymer Solutions: A Computer Simulation Study
We study single-chain motion in semidilute solutions of polymers of length N
= 1000 with excluded-volume and hydrodynamic interactions by a novel algorithm.
The crossover length of the transition from Zimm (short lengths and times) to
Rouse dynamics (larger scales) is proportional to the static screening length.
The crossover time is the corresponding Zimm time. Our data indicate Zimm
behavior at large lengths but short times. There is no hydrodynamic screening
until the chains feel constraints, after which they resist the flow:
"Incomplete screening" occurs in the time domain.Comment: 3 figure
Intrinsic profiles and capillary waves at homopolymer interfaces: a Monte Carlo study
A popular concept which describes the structure of polymer interfaces by
``intrinsic profiles'' centered around a two dimensional surface, the ``local
interface position'', is tested by extensive Monte Carlo simulations of
interfaces between demixed homopolymer phases in symmetric binary (AB)
homopolymer blends, using the bond fluctuation model. The simulations are done
in an LxLxD geometry. The interface is forced to run parallel to the LxL planes
by imposing periodic boundary conditions in these directions and fixed boundary
conditions in the D direction, with one side favoring A and the other side
favoring B. Intrinsic profiles are calculated as a function of the ``coarse
graining length'' B by splitting the system into columns of size BxBxD and
averaging in each column over profiles relative to the local interface
position. The results are compared to predictions of the self-consistent field
theory. It is shown that the coarse graining length can be chosen such that the
interfacial width matches that of the self-consistent field profiles, and that
for this choice of B the ``intrinsic'' profiles compare well with the
theoretical predictions.Comment: to appear in Phys. Rev.
Randomly Crosslinked Macromolecular Systems: Vulcanisation Transition to and Properties of the Amorphous Solid State
As Charles Goodyear discovered in 1839, when he first vulcanised rubber, a
macromolecular liquid is transformed into a solid when a sufficient density of
permanent crosslinks is introduced at random. At this continuous equi- librium
phase transition, the liquid state, in which all macromolecules are
delocalised, is transformed into a solid state, in which a nonzero fraction of
macromolecules have spontaneously become localised. This solid state is a most
unusual one: localisation occurs about mean positions that are distributed
homogeneously and randomly, and to an extent that varies randomly from monomer
to monomer. Thus, the solid state emerging at the vulcanisation transition is
an equilibrium amorphous solid state: it is properly viewed as a solid state
that bears the same relationship to the liquid and crystalline states as the
spin glass state of certain magnetic systems bears to the paramagnetic and
ferromagnetic states, in the sense that, like the spin glass state, it is
diagnosed by a subtle order parameter.
In this review we give a detailed exposition of a theoretical approach to the
physical properties of systems of randomly, permanently crosslinked
macromolecules. Our primary focus is on the equilibrium properties of such
systems, especially in the regime of Goodyear's vulcanisation transition.Comment: Review Article, REVTEX, 58 pages, 3 PostScript figure
Temperature and magnetic field dependence of the lattice constant in spin-Peierls cuprate CuGeO_3 studied by capacitance dilatometry in fields up to 16 Tesla
We present high resolution measurements of the thermal expansion coefficient
and the magnetostriction along the a-axis of CuGeO_3 in magnetic fields up to
16 Tesla. From the pronounced anomalies of the lattice constant a occurring for
both temperature and field induced phase transitions clear structural
differences between the uniform, dimerized, and incommensurate phases are
established. A precise field temperature phase diagram is derived and compared
in detail with existing theories. Although there is a fair agreement with the
calculations within the Cross Fisher theory, some significant and systematic
deviations are present. In addition, our data yield a high resolution
measurement of the field and temperature dependence of the spontaneous strain
scaling with the spin-Peierls order parameter. Both the zero temperature values
as well as the critical behavior of the order parameter are nearly field
independent in the dimerized phase. A spontaneous strain is also found in the
incommensurate high field phase, which is significantly smaller and shows a
different critical behavior than that in the low field phase. The analysis of
the temperature dependence of the spontaneous strain yields a pronounced field
dependence within the dimerized phase, whereas the temperature dependence of
the incommensurate lattice modulation compares well with that of the
dimerization in zero magnetic field.Comment: 25 pages, 15 Figs., to appear in Phys. Rev. B55 (Vol.5
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