The observed UV rest-frame spectra of distant galaxies are the result of their intrinsic emission combined with absorption along the line of sight produced by the inter-galactic medium (IGM). Here we ...analyse the evolution of the mean IGM transmission Tr(Lyα) and its dispersion along the line of sight for 2127 galaxies with 2.5 < z < 5.5 in the VIMOS Ultra Deep Survey (VUDS). We fitted model spectra combined with a range of IGM transmission to the galaxy spectra using the spectral fitting algorithm GOSSIP+. We used these fits to derive the mean IGM transmission towards each galaxy for several redshift slices from z = 2.5 to z = 5.5. We found that the mean IGM transmission defined as Tr(Lyα) = e− τ (with τ as the HI optical depth) is 79%, 69%, 59%, 55%, and 46% at redshifts 2.75, 3.22, 3.70, 4.23, and 4.77, respectively. We compared these results to measurements obtained from quasar lines of sight and found that the IGM transmission towards galaxies is in excellent agreement with quasar values up to redshift z ~ 4. We found tentative evidence for a higher IGM transmission at z ≥ 4 compared to results from QSOs, but a degeneracy between dust extinction and IGM prevents us from firmly concluding whether the internal dust extinction for star-forming galaxies at z > 4 takes a mean value significantly in excess of E(B−V) > 0.15. Most importantly, we found a large dispersion of IGM transmission along the lines of sight towards distant galaxies with 68% of the distribution within 10 to 17% of the median value in δz = 0.5 bins, similar to what is found on the lines of sight towards QSOs. We demonstrate that taking this broad range of IGM transmission into account is important when selecting high-redshift galaxies based on their colour properties (e.g. LBG or photometric redshiftselection) because failing to do so causes a significant incompleteness in selecting high-redshift galaxy populations. We finally discuss the observed IGM properties and speculate that the broad range of observed transmissions might be the result of cosmic variance and clustering along lines of sight. This clearly shows that the sources that cause this extinction need to be more completely modelled.
We investigate the effect of different star formation histories (SFHs) on the relation between stellar mass (M∗) and star formation rate (SFR) using a sample of galaxies with reliable spectroscopic ...redshift zspec> 2 drawn from the VIMOS Ultra-Deep Survey (VUDS). We produce an extensive database of dusty model galaxies, calculated starting from a new library of single stellar population (SSPs) models, weighted by a set of 28 different star formation histories based on the Schmidt function, and characterized by different ratios of the gas infall timescale τinfall to the star formation efficiency ν. Dust extinction and re-emission were treated by means of the radiative transfer calculation. The spectral energy distribution (SED) fitting technique was performed by using GOSSIP+, a tool able to combine both photometric and spectroscopic information to extract the best value of the physical quantities of interest, and to consider the intergalactic medium (IGM) attenuation as a free parameter. We find that the main contribution to the scatter observed in the SFR-M∗ plane is the possibility of choosing between different families of SFHs in the SED fitting procedure, while the redshift range plays a minor role. The majority of the galaxies, at all cosmic times, are best fit by models with SFHs characterized by a high τinfall/ν ratio. We discuss the reliability of a low percentage of dusty and highly star-forming galaxies in the context of their detection in the far infrared (FIR).
Characterizing railroad ballast behavior under repeated train loading is of significant importance for evaluating field settlement or permanent deformation potentials of unbound aggregate ballast ...layers. For the proper characterization of ballast behavior under dynamic loading, a new triaxial test setup was recently developed at the University of Illinois at Urbana–Champaign. Capable of accommodating cylindrical specimens with a diameter of 305 mm (12 in.) and a height of 610 mm (24 in.), this closed-loop servohydraulic test setup used a load cell and four displacement transducers mounted on the specimen to quantify deformation behavior under loading. Preliminary test results evaluating effects of different applied stress states as well as geogrid reinforcement on ballast behavior established the consistency and repeatability of this new test equipment. Laboratory findings are presented from an ongoing research study aimed at investigating the effects of different ballast types and field degradation trends on permanent deformation accumulation. The ballast type with the highest mill abrasion value was found to accumulate the highest permanent deformation under repeated load triaxial testing. Permanent deformation trends observed for four other ballast types showed direct correlations to the degrees of particle degradation observed in track sections constructed with these ballast materials and trafficked for approximately 18 months with a total track usage of 320 million gross tons.
We investigate the evolution of galaxy clustering for galaxies in the redshift range 2.0 <z< 5.0 using the VIMOS Ultra Deep Survey (VUDS). We present the projected (real-space) two-point correlation ...function wp(rp) measured by using 3022 galaxies with robust spectroscopic redshifts in two independent fields (COSMOS and VVDS-02h) covering in total 0.8deg2. We quantify how the scale dependent clustering amplitude r0 changes with redshift making use of mock samples to evaluate and correct the survey selection function. Using a power-law model ξ(r) = (r/r0)− γ we find that the correlation function for the general population is best fit by a model with a clustering length r0 = 3.95+0.48-0.54 h-1 Mpc and slope γ = 1.8+0.02-0.06 at z ~ 2.5, r0 = 4.35 ± 0.60 h-1 Mpc and γ = 1.6+0.12-0.13 at z ~ 3.5. We use these clustering parameters to derive the large-scale linear galaxy bias bLPL, between galaxies and dark matter. We find bLPL = 2.68 ± 0.22 at redshift z ~ 3 (assuming σ8 = 0.8), significantly higher than found at intermediate and low redshifts for the similarly general galaxy populations. We fit a halo occupation distribution (HOD) model to the data and we obtain that the average halo mass at redshift z ~ 3 is Mh = 1011.75 ± 0.23 h-1M⊙. From this fit we confirm that the large-scale linear galaxy bias is relatively high at bLHOD = 2.82 ± 0.27. Comparing these measurements with similar measurements at lower redshifts we infer that the star-forming population of galaxies at z ~ 3 should evolve into the massive and bright (Mr< −21.5)galaxy population, which typically occupy haloes of mass ⟨ Mh ⟩ = 1013.9 h-1M⊙ at redshift z = 0.
An automotive electric-power-steering synchronous machine driven from a multifunctional converter has the advantage of increased system voltage. The integration of the boost converter in the inverter ...and the electrical machine leads to new requirements for the machine design due to dc currents and increased high-frequency ripple currents in the motor windings. In this paper, the ripple currents of a synchronous machine with a multifunctional converter are investigated. Three winding arrangements are analyzed and compared to reduce the ripple currents together with interleaved pulsewidth modulation. This paper contains finite-element simulations of the zero-sequence flux and analyses of the ripple currents with and without low-frequency ac modulation and, hence, when operated at high and low rotational speed. The magnitude of the ripple current depends on the zero-sequence inductance. By rearranging the coils in the stator slots, the zero-sequence inductance is significantly increased. Experimental results are correlating well with theoretical predictions and demonstrate that the phase and star-point ripple currents are almost halved.
The relation between the galaxy stellar mass M⋆ and the dark matter halo mass Mh gives important information on the efficiency in forming stars and assembling stellar mass in galaxies. We present ...measurements of the ratio of stellar mass to halo mass (SMHR) at redshifts 2 < z < 5, obtained from the VIMOS Ultra Deep Survey. We use halo occupation distribution (HOD) modelling of clustering measurements on ~3000 galaxies with spectroscopic redshifts to derive the dark matter halo mass Mh, and spectral energy density fitting over a large set of multi-wavelength data to derive the stellar mass M⋆ and compute the SMHR = M⋆/Mh. We find that the SMHR ranges from 1% to 2.5% for galaxies with M⋆ = 1.3 × 109 M⊙ to M⋆ = 7.4 × 109 M⊙ in DM halos with Mh = 1.3 × 1011 M⊙ to Mh = 3 × 1011 M⊙. We derive the integrated star formation efficiency (ISFE) of these galaxies and find that the star formation efficiency is a moderate 6−9% for lower mass galaxies, while it is relatively high at 16% for galaxies with the median stellar mass of the sample ~ 7 × 109 M⊙. The lower ISFE at lower masses may indicate that some efficient means of suppressing star formation is at work (like SNe feedback), while the high ISFE for the average galaxy at z ~ 3 indicates that these galaxies efficiently build up their stellar mass at a key epoch in the mass assembly process. Based on our results, we propose a possible scenario in which the average massive galaxy at z ~ 3 begins to experience truncation of its star formation within a few million years.
Context. The size of a galaxy encapsulates the signature of the different physical processes driving its evolution. The distribution of galaxy sizes in the Universe as a function of cosmic time is ...therefore a key to understand galaxy evolution. Aims. We aim to measure the average sizes and size distributions of galaxies as they are assembling before the peak in the comoving star formation rate density of the Universe to better understand the evolution of galaxies across cosmic time. Methods. We used a sample of similar to 1200 galaxies in the COSMOS and ECDFS fields with confirmed spectroscopic redshifts 2 \textless= z(spec) \textless= 4 : 5 in the VIMOS Ultra Deep Survey (VUDS), representative of star-forming galaxies with i(AB) \textless= 25. We first derived galaxy sizes by applying a classical parametric profile-fitting method using GALFIT. We then measured the total pixel area covered by a galaxy above a given surface brightness threshold, which overcomes the difficulty of measuring sizes of galaxies with irregular shapes. We then compared the results obtained for the equivalent circularized radius enclosing 100% of the measured galaxy light r(T)(100) to those obtained with the effective radius re; circ measured with GALFIT. Results. We find that the sizes of galaxies computed with our non-parametric approach span a wide range but remain roughly constant on average with a median value r(T)(100) similar to 2 : 2 kpc for galaxies with 2 \textless z \textless 4 : 5. This is in stark contrast with the strong downward evolution of r(e) with increasing redshift, down to sizes of \textless 1 kpc at z similar to 4 : 5. We analyze the difference and find that parametric fitting of complex, asymmetric, multicomponent galaxies is severely underestimating their sizes. By comparing r(T)(100) with physical parameters obtained through fitting the spectral energy distribution we find that the star-forming galaxies that are the largest at any redshift are, on average, more massive and form more stars. We discover that galaxies present more concentrated light profiles with increasing redshifts. We interpret these results as the signature of several, possibly different, evolutionary paths of galaxies in their early stages of assembly, including major and minor merging or star formation in multiple bright regions.
Roller-compacted concrete (RCC) pavement has renewed interest among designers as a sustainable pavement option with the potential to lower total cement content, incorporate recycled aggregates, ...reduce road closure time, and decrease total project costs. One main design challenge is whether RCC can achieve the same performance life as conventional portland cement concrete (PCC) pavement with similar slab thickness. This research investigated the strength and fracture properties of RCC containing virgin aggregates and fractionated reclaimed asphalt pavement (FRAP) relative to conventional PCC to address this design challenge. The compressive and split tensile strengths of the RCC mixes showed similar strengths to the same constituents in PCC. RCC containing FRAP had lower strengths than did RCC with virgin aggregates. The critical stress intensity factor and the initial and total fracture energies were not statistically different between the RCC mixes containing virgin and FRAP aggregates. Overall, the RCC fracture properties were found to be significantly higher than those of conventional PCC. At lower stress ratios, RCC fatigue data from laboratory beam tests predict lower fatigue life relative to PCC; this result translates to a thicker RCC pavement. Large-scale testing has shown that the flexural capacity of PCC slabs is strongly related to the concrete fracture properties despite differences in beam flexural strength. Because these RCC fracture properties were shown to be higher than similar constituents used in conventional paving concrete, RCC designs could employ similar PCC fatigue curves for certain conditions, such as when the RCC fracture properties are equivalent to or greater than those of conventional PCC.
The relation between the galaxy stellar mass M-star and the dark matter halo mass M-h gives important information on the efficiency in forming stars and assembling stellar mass in galaxies. We ...present measurements of the ratio of stellar mass to halo mass (SMHR) at redshifts 2 \textless z \textless 5, obtained from the VIMOS Ultra Deep Survey. We use halo occupation distribution (HOD) modelling of clustering measurements on similar to 3000 galaxies with spectroscopic redshifts to derive the dark matter halo mass M-h, and spectral energy density fitting over a large set of multi-wavelength data to derive the stellar mass M-star and compute the SMHR = M-star/M-h. We find that the SMHR ranges from 1% to 2.5% for galaxies with M-star = 1.3 x 10(9) M-star to M-star = 7.4 x 10(9) M-circle dot in DM halos with M-h = 1.3 x 10(11) M-circle dot to M-h = 3 x 10(11) M-circle dot. We derive the integrated star formation efficiency (ISFE) of these galaxies and find that the star formation efficiency is a moderate 6-9% for lower mass galaxies, while it is relatively high at 16% for galaxies with the median stellar mass of the sample similar to 7 x 10(9) M-circle dot. The lower ISFE at lower masses may indicate that some efficient means of suppressing star formation is at work (like SNe feedback), while the high ISFE for the average galaxy at z similar to 3 indicates that these galaxies efficiently build up their stellar mass at a key epoch in the mass assembly process. Based on our results, we propose a possible scenario in which the average massive galaxy at z similar to 3 begins to experience truncation of its star formation within a few million years.
We analyse a sample of 23 supermassive elliptical galaxies (central velocity dispersion larger than 330kms-1) drawn from the Sloan Digital Sky Survey. For each object, we estimate the dynamical mass ...from the light profile and central velocity dispersion, and compare it with the stellar mass derived from stellar population models. We show that these galaxies are dominated by luminous matter within the radius for which the velocity dispersion is measured. We find that the sizes and stellar masses are tightly correlated, with Re proportional to M1.1*, making the mean density within the de Vaucouleurs radius a steeply declining function of M*: rho e proportional to M-2.2*. These scalings are easily derived from the virial theorem if one recalls that this sample has essentially fixed (but large) sigma 0. In contrast, the mean density within 1kpc is almost independent of M*, at a value that is in good agreement with recent studies of z similar to 2 galaxies. The fact that the mass within 1kpc has remained approximately unchanged suggests assembly histories that were dominated by minor mergers - but we discuss why this is not the unique way to achieve this. Moreover, the total stellar mass of the objects in our sample is typically a factor of similar to 5 larger than that in the high-redshift (z similar to 2) sample, an amount which seems difficult to achieve. If our galaxies are the evolved objects of the recent high-redshift studies, then we suggest that major mergers are required at zgap 1.5 and that minor mergers become the dominant growth mechanism for massive galaxies at zlap 1.5.
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