3,546 research outputs found
Cost and benefit of energy efficient buildings
Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Mechanical Engineering, 2006.Includes bibliographical references.A common misconception among developers and policy-makers is that "sustainable buildings" may not be financially justified. However, this report strives to show that building green is cost-effective and does make financial sense today. Though green buildings typically have a higher upfront cost compared to conventional constructions, they do offer benefits that simply built-to-code projects lack. These benefits include cost savings from reduced energy and water use, less waste production, diminished environmental and emissions costs, lower operations and maintenance costs, and enhanced occupant productivity and health. These values range from being fairly predictable (energy and water savings can be recorded over time) to relatively uncertain (productivity/health benefits are somewhat arbitrary and subjective). Based on a 20-year Net Present Value analysis with a 5% real interest rate, a recent study by the California Sustainable Energy Task Force showed the total financial benefits of green design to be 75/ft2, depending on the building's level of LEED Certification. This number is over ten times bigger than the average 2% cost premium calculated for the 33 green buildings they analyzed-about 5.79, which already exceeds the cost premium. Conservative calculations based on a study on Norway building retrofits show that the cost of energy savings ranges from 1-4 cents/kWh. Comparing this number to the cost of various modes of electricity generation, ranging from 3-80 cents/kWh, it is clear that the cost of generating electricity greatly exceeds the cost of saving energy through energy efficient buildings. Thus, green buildings are cost effective and should be more widely adopted.by Wenying Zhang.S.B
Resistance to ACCase-inhibiting herbicides in sprangletop (Leptochloa chinensis)
This study reports evolved resistance to fenoxaprop-P in a population of sprangletop from a rice field in Thailand (BLC1). After eight applications of fenoxaprop-P, the herbicide appeared no longer effective. To confirm herbicide resistance in the BLC1 population, three experiments were conducted. First, glasshouse experiments revealed that the BLC1 population survived 600 g ai ha-1 of fenoxaprop-P without visual injury. Second, the BLC1 population was treated with fenoxaprop-P and other acetyl coenzyme A carboxylase (ACCase)-inhibiting herbicides (quizalofop-P, cyhalofopbutyl, and profoxydim) under field conditions; BLC1 exhibited resistance to all of these herbicides. Third, seeds of susceptible SLC1 and resistant BLC1 were germinated on 0.6% (v/v) agar across a range of herbicide concentrations. The resistant BLC1 population exhibited 61-, 44-, 9- and 8-fold resistance to fenoxaprop-P, cyhalofop, quizalofop-P, and profoxydim, respectively, compared with a susceptible SLC1 population. At the enzyme level, ACCase from the resistant BLC1 exhibited 30, 24, 11, 4, and 5 times resistance to fenoxaprop, cyhalofop-butyl, haloxyfop, clethodim, and cycloxydim, respectively. The spectrum of resistance at the whole plant level correlated well with resistance at the ACCase level. Hence, the mechanism of resistance to ACCase-inhibiting herbicides in this biotype of sprangletop is a herbicide-resistant ACCase. The specific mutation(s) of the ACCase gene that endows resistance in this population remains to be investigated
5 7 5 line defects on As Si 100 A general stress relief mechanism for V IV surfaces
An entire family of nano scale trenches, ridges, and steps has been observed experimentally on AsH3 exposed Si 100 . Some of these line structures have been observed previously, but their structures have remained a mystery. Theoretical modeling shows that they are all based upon the same stress relieving 5 7 5 core structure. The strong similarities between line structures on As Si 100 , P Si 100 , As Ge 100 , and other V IV surfaces lead to a much broader conclusion 5 7 5 line structures are a general form of stress relief for group V terminated Si and Ge surface
Multi-locus phylogeny of Pleosporales: a taxonomic, ecological and evolutionary re-evaluation
Five loci, nucSSU, nucLSU rDNA, TEF1, RPB1 and RPB2, are used for analysing 129 pleosporalean taxa representing 59 genera and 15 families in the current classification of Pleosporales. The suborder Pleosporineae is emended to include four families, viz. Didymellaceae, Leptosphaeriaceae, Phaeosphaeriaceae and Pleosporaceae. In addition, two new families are introduced, i.e. Amniculicolaceae and Lentitheciaceae. Pleomassariaceae is treated as a synonym of Melanommataceae, and new circumscriptions of Lophiostomataceae s. str, Massarinaceae and Lophiotrema are proposed. Familial positions of Entodesmium and Setomelanomma in Phaeosphaeriaceae, Neophaeosphaeria in Leptosphaeriaceae, Leptosphaerulina, Macroventuria and Platychora in Didymellaceae, Pleomassaria in Melanommataceae and Bimuria, Didymocrea, Karstenula and Paraphaeosphaeria in Montagnulaceae are clarified. Both ecological and morphological characters show varying degrees of phylogenetic significance. Pleosporales is most likely derived from a saprobic ancestor with fissitunicate asci containing conspicuous ocular chambers and apical rings. Nutritional shifts in Pleosporales likely occured from saprotrophic to hemibiotrophic or biotrophic
Ferromagnetism in Mn doped GaAs due to substitutional-interstitial complexes
While most calculations on the properties of the ferromagnetic semiconductor
GaAs:Mn have focussed on isolated Mn substituting the Ga site (Mn), we
investigate here whether alternate lattice sites are favored and what the
magnetic consequences of this might be. Under As-rich (Ga-poor) conditions
prevalent at growth, we find that the formation energies are lower for
Mn over interstitial Mn (Mn).As the Fermi energy is shifted towards
the valence band maximum via external -doping, the formation energy of
Mn is reduced relative to Mn. Furthermore, under epitaxial growth
conditions, the solubility of both substitutional and interstitial Mn are
strongly enhanced over what is possible under bulk growth conditions. The high
concentration of Mn attained under epitaxial growth of p-type material opens
the possibility of Mn atoms forming small clusters. We consider various types
of clusters, including the Coulomb-stabilized clusters involving two Mn
and one Mn. While isolated Mn are hole killers (donors), and therefore
destroy ferromagnetism,complexes such as Mn-Mn-Mn) are found
to be more stable than complexes involving Mn-Mn-Mn. The
former complexes exhibit partial or total quenching of holes, yet Mn in
these complexes provide a channel for a ferromagnetic arrangement of the spins
on the two Mn within the complex. This suggests that ferromagnetism in
Mn doped GaAs arises both from holes due to isolated Mn as well as from
strongly Coulomb stabilized Mn-Mn-Mn clusters.Comment: 7 figure
Adaptive Sampling Approach to the Negative Sign Problem in the Auxiliary Field Quantum Monte Carlo Method
We propose a new sampling method to calculate the ground state of interacting
quantum systems. This method, which we call the adaptive sampling quantum monte
carlo (ASQMC) method utilises information from the high temperature density
matrix derived from the monte carlo steps. With the ASQMC method, the negative
sign ratio is greatly reduced and it becomes zero in the limit
goes to zero even without imposing any constraint such like the constraint path
(CP) condition. Comparisons with numerical results obtained by using other
methods are made and we find the ASQMC method gives accurate results over wide
regions of physical parameters values.Comment: 8 pages, 7 figure
Towards Reliable Automatic Protein Structure Alignment
A variety of methods have been proposed for structure similarity calculation,
which are called structure alignment or superposition. One major shortcoming in
current structure alignment algorithms is in their inherent design, which is
based on local structure similarity. In this work, we propose a method to
incorporate global information in obtaining optimal alignments and
superpositions. Our method, when applied to optimizing the TM-score and the GDT
score, produces significantly better results than current state-of-the-art
protein structure alignment tools. Specifically, if the highest TM-score found
by TMalign is lower than (0.6) and the highest TM-score found by one of the
tested methods is higher than (0.5), there is a probability of (42%) that
TMalign failed to find TM-scores higher than (0.5), while the same probability
is reduced to (2%) if our method is used. This could significantly improve the
accuracy of fold detection if the cutoff TM-score of (0.5) is used.
In addition, existing structure alignment algorithms focus on structure
similarity alone and simply ignore other important similarities, such as
sequence similarity. Our approach has the capacity to incorporate multiple
similarities into the scoring function. Results show that sequence similarity
aids in finding high quality protein structure alignments that are more
consistent with eye-examined alignments in HOMSTRAD. Even when structure
similarity itself fails to find alignments with any consistency with
eye-examined alignments, our method remains capable of finding alignments
highly similar to, or even identical to, eye-examined alignments.Comment: Peer-reviewed and presented as part of the 13th Workshop on
Algorithms in Bioinformatics (WABI2013
A Note on Chern-Simons Solitons - a type III vortex from the wall vortex
We study some properties of topological Chern-Simons vortices in 2 + 1
dimensions. As has already been understood in the past, in the large magnetic
flux limit, they are well described by a Chern-Simons domain wall, which has
been compactified on a circle with the symmetric phase inside and the
asymmetric phase on the outside. Our goal is two-fold. First we want to explore
how the tension depends on the magnetic flux discretized by the integer n. The
BPS case is already known, but not much has been explored about the non-BPS
potentials. A generic renormalizable potential has two dimensionless parameters
that can be varied. Variation of only one of them lead to a type I and type II
vortex, very similar to the Abrikosov-Nielsen-Olesen (ANO) case. Variation of
both the parameters leads to a much richer structure. In particular we have
found a new type of vortex, which is type I-like for small flux and then turns
type II-like for larger flux. We could tentatively denote it a type III vortex.
This results in a stable vortex with number of fluxes which can be greater than
one. Our second objective is to study the Maxwell-Chern-Simons theory and and
understand how the large n limit of the CS vortex is smoothly connected with
the large n limit of the ANO vortex.Comment: 27 pages, 17 figures; v2.: references added, subsection 3.2 added,
explanation added in section 2.
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