203 research outputs found
Effective Lengths of Web Members in Trusses - an Experimental Investigation of Tension Effects
Throughout the truss and joist industry, research is constantly underway in an effort to determine ways to further minimize production costs and material use. In regard to structural stability, previous research has shown that the effective length factor, K, for web members may be overly conservative, leading to an overuse of material in the design. Currently, the top and bottom chords provide the only acknowledged flexural and torsional resistance for compression web members in trusses. This study presents an investigation into the restraining effects provided by tension members in trusses, which is in an effort to determine whether the tensioning effect is adequate to warrant the use of a smaller K-factor in routine design. Two different methods to explore the buckling mode of compression web members are performed for this research, including (1) the use of an experimental testing apparatus, and (2) computational analysis of compression web members within a modified Pratt truss. The results are presented and summarized based on the nature of the research method. Results of the experimental testing confirmed the presence of additional rotational restraint provided by tension members. Therefore, it was concluded that effective length factors for compression web members need not exceed a value of 1.0. The computational studies of a modified Pratt truss supported this conclusion and further suggest that a K-factor of less than 1.0 could be used in design, provided that sufficient resistance to out-of-plane translation is present along the bottom chord (via bracing or other means). Recommendations for future work, including full-scale testing and additional computational studies, are provided within this thesis
Word-Finding Difficulties: Exploring Tip-of-the-Tongue States in Young and Old Adults
A Tip-of-the-Tongue (TOT) occurs when you are trying to think of a specific word but lack the ability to bring it to mind. The present study examined implicit learning processes operating under errorful (20-second delay) or errorless (0-second delay) learning conditions in TOT states. Participants included 15 young (20-30 years) and 15 old (65-88 years) adults who were tested twice a week for four weeks on a definition-word pair task. For young participants, results indicated that a TOT was more likely and older participants were more likely to indicate they did not know the word on a consecutive session after a 0-second delay. Over multiple sessions, older participants were more likely to resolve after persisting in a TOT state for 20-seconds. Results are inconsistent with the view that the longer people spend practicing an incorrect pathway, the more likely they are to experience a TOT on the next session. Rather, the findings suggest that remaining in a TOT state and purposefully searching for the word may facilitate word finding, at least in the short term
Evidence of Lensing of the Cosmic Microwave Background by Dark Matter Halos
We present evidence of the gravitational lensing of the cosmic microwave background by 1013 solar mass dark matter halos. Lensing convergence maps from the Atacama Cosmology Telescope Polarimeter (ACTPol) are stacked at the positions of around 12 000 optically selected CMASS galaxies from the SDSS-III/BOSS survey. The mean lensing signal is consistent with simulated dark matter halo profiles and is favored over a null signal at 3.2σsignificance. This result demonstrates the potential of microwave background lensing to probe the dark matter distribution in galaxy group and galaxy cluster halos
The Atacama Cosmology Telescope: measuring radio galaxy bias through cross-correlation with lensing
We correlate the positions of radio galaxies in the FIRST survey with the cosmic microwave background lensing convergence estimated from the Atacama Cosmology Telescope over 470 deg2 to determine the bias of these galaxies. We remove optically cross-matched sources below redshiftz = 0.2 to preferentially select active galactic nuclei (AGN). We measure the angular cross-power spectrum Cκgl at 4.4σ significance in the multipole range 100 \u3c l \u3c 3000, corresponding to physical scales within ≈2–60 Mpc at an effective redshift zeff = 1.5. Modelling the AGN population with a redshift-dependent bias, the cross-spectrum is well fitted by the Planck best-fitting Λ cold dark matter cosmological model. Fixing the cosmology and assumed redshift distribution of sources, we fit for the overall bias model normalization, finding b(zeff) = 3.5 ± 0.8 for the full galaxy sample and b(zeff) = 4.0 ± 1.1(3.0 ± 1.1) for sources brighter (fainter) than 2.5 mJy. This measurement characterizes the typical halo mass of radio-loud AGN: we find log(Mhalo/M⊙)=13.6+0.3−0.4
Collective behavior of interacting self-propelled particles
We discuss biologically inspired, inherently non-equilibrium self-propelled
particle models, in which the particles interact with their neighbours by
choosing at each time step the local average direction of motion. We summarize
some of the results of large scale simulations and theoretical approaches to
the problem
Dopaminergic medication impairs feedback-based stimulus-response learning but not response selection in Parkinson\u27s disease.
Cognitive dysfunction is a feature of Parkinson\u27s Disease (PD). Some cognitive functions are impaired by dopaminergic medications prescribed to address the movement symptoms that typify PD. Learning appears to be the cognitive function most frequently worsened by dopaminergic therapy. However, this result could reflect either impairments in learning (i.e., acquisition of associations among stimuli, responses, and outcomes) or deficits in performance based on learning (e.g., selecting responses). We sought to clarify the specific effects of dopaminergic medication on (a) stimulus-response association learning from outcome feedback and (b) response selection based on learning, in PD. We tested 28 PD patients on and/or off dopaminergic medication along with 32 healthy, age- and education-matched controls. In Session 1, participants learned to associate abstract images with specific key-press responses through trial and error via outcome feedback. In Session 2, participants provided specific responses to abstract images learned in Session 1, without feedback, precluding new feedback-based learning. By separating Sessions 1 and 2 by 24 h, we could distinguish the effect of dopaminergic medication on (a) feedback-based learning and response selection processes in Session 1 as well as on (b) response selection processes when feedback-based learning could not occur in Session 2. Accuracy achieved at the end of Session 1 were comparable across groups. PD patients on medication learned stimulus-response associations more poorly than PD patients off medication and controls. Medication did not influence decision performance in Session 2. We confirm that dopaminergic therapy impairs feedback-based learning in PD, discounting an alternative explanation that warranted consideration
Radiative association and inverse predissociation of oxygen atoms
The formation of \mbox{O}_2 by radiative association and by inverse
predissociation of ground state oxygen atoms is studied using
quantum-mechanical methods. Cross sections, emission spectra, and rate
coefficients are presented and compared with prior experimental and theoretical
results. At temperatures below 1000~K radiative association occurs by approach
along the state of \mbox{O}_2 and above 1000~K inverse
predissociation through the \mbox{B}\,{}^3\Sigma_u^- state is the dominant
mechanism. This conclusion is supported by a quantitative comparison between
the calculations and data obtained from hot oxygen plasma spectroscopy.Comment: submitted to Phys. Rev. A (Sept. 7., 1994), 19 pages, 4 figures,
latex (revtex3.0 and epsf.sty
Recommended from our members
Vibration Stabilization of a Mechanical Model of a X-Band Linear Collider Final Focus Magnet
The small beam sizes at the interaction point of a X-band linear collider require mechanical stabilization of the final focus magnets at the nanometer level. While passive systems provide adequate performance at many potential sites, active mechanical stabilization is useful if the natural or cultural ground vibration is higher than expected. A mechanical model of a room temperature linear collider final focus magnet has been constructed and actively stabilized with an accelerometer based system
The Atacama Cosmology Telescope: Two-Season ACTPol Spectra and Parameters
We present the temperature and polarization angular power spectra measured by
the Atacama Cosmology Telescope Polarimeter (ACTPol). We analyze night-time
data collected during 2013-14 using two detector arrays at 149 GHz, from 548
deg of sky on the celestial equator. We use these spectra, and the spectra
measured with the MBAC camera on ACT from 2008-10, in combination with Planck
and WMAP data to estimate cosmological parameters from the temperature,
polarization, and temperature-polarization cross-correlations. We find the new
ACTPol data to be consistent with the LCDM model. The ACTPol
temperature-polarization cross-spectrum now provides stronger constraints on
multiple parameters than the ACTPol temperature spectrum, including the baryon
density, the acoustic peak angular scale, and the derived Hubble constant.
Adding the new data to planck temperature data tightens the limits on damping
tail parameters, for example reducing the joint uncertainty on the number of
neutrino species and the primordial helium fraction by 20%.Comment: 23 pages, 25 figure
Detailed SZ study of 19 LoCuSS galaxy clusters: masses and temperatures out to the virial radius
We present 16-GHz AMI SZ observations of 19 clusters with L_X >7x10^37 W
(h50=1) selected from the LoCuS survey (0.142<z<0.295) and of A1758b, in the
FoV of A1758a. We detect 17 clusters with 5-23sigma peak surface brightnesses.
Cluster parameters are obtained using a Bayesian cluster analysis. We fit
isothermal beta-models to our data and assume the clusters are virialized (with
all the kinetic energy in gas internal energy). Our gas temperature, T_AMI, is
derived from AMI SZ data, not from X-ray spectroscopy. Cluster parameters
internal to r500 are derived assuming HSE. We find: (i) Different gNFW
parameterizations yield significantly different parameter degeneracies. (ii)
For h70 = 1, we find the virial radius r200 to be typically 1.6+/-0.1 Mpc and
the total mass M_T(r200) typically to be 2.0-2.5xM_T(r500).(iii) Where we have
found M_T X-ray (X) and weak-lensing (WL) values in the literature, there is
good agreement between WL and AMI estimates (with M_{T,AMI}/M_{T,WL}
=1.2^{+0.2}_{-0.3} and =1.0+/-0.1 for r500 and r200, respectively). In
comparison, most Suzaku/Chandra estimates are higher than for AMI (with
M_{T,X}/M_{T,AMI}=1.7+/-0.2 within r500), particularly for the stronger
mergers.(iv) Comparison of T_AMI to T_X sheds light on high X-ray masses: even
at large r, T_X can substantially exceed T_AMI in mergers. The use of these
higher T_X values will give higher X-ray masses. We stress that large-r T_SZ
and T_X data are scarce and must be increased. (v) Despite the paucity of data,
there is an indication of a relation between merger activity and SZ
ellipticity. (vi) At small radius (but away from any cooling flow) the SZ
signal (and T_AMI) is less sensitive to ICM disturbance than the X-ray signal
(and T_X) and, even at high r, mergers affect n^2-weighted X-ray data more than
n-weighted SZ, implying significant shocking or clumping or both occur even in
the outer parts of mergers.Comment: 45 pages, 33 figures, 13 tables Accepted for publication in MNRA
- …