Envelope Scale Research Articles

Effects of Magnetic Field Orientations in Dense Cores on Gas Kinematics in Protostellar Envelopes

Theoretically, misalignment between the magnetic field and rotational axis in a dense core is considered to be dynamically important in the star formation process; however, the extent of this influence remains observationally unclear. For a sample of 32 Class 0 and I protostars in the Perseus Molecular Cloud, we analyzed gas motions using C18O data from the SMA MASSES survey and the magnetic field structures using 850 μm polarimetric data from the JCMT BISTRO-1 survey and archive. We do not find any significant correlation between the velocity gradients in the C18O emission in the protostellar envelopes at a 1000 au scale and the misalignment between the outflows and magnetic field orientations in the dense cores at a 4000 au scale, and there is also no correlation between the velocity gradients and the angular dispersions of the magnetic fields. However, a significant dependence on the misalignment angles emerges after we normalize the rotational motion by the infalling motion, where the ratios increase from ≲1 to ≳1 with increasing misalignment angle. This suggests that the misalignment could prompt angular momentum transportation to the envelope scale but is not a dominant factor in determining the envelope rotation, and other parameters, such as mass accretion in protostellar sources, also play an important role. These results remain valid after taking into account projection effects. The comparison between our estimated angular momentum in the protostellar envelopes and the sizes of the known protostellar disks suggests that significant angular momentum is likely lost between radii of ∼1000 and 100 au in protostellar envelopes.

The transition of polarized dust thermal emission from the protostellar envelope to the disc scale

ABSTRACT Polarized dust continuum emission has been observed with Atacama Large Millimeter/submillimeter Array in an increasing number of deeply embedded protostellar systems. It generally shows a sharp transition going from the protostellar envelope to the disc scale, with the polarization fraction typically dropping from ${\sim } 5{{\ \rm per\ cent}}$ to ${\sim } 1{{\ \rm per\ cent}}$ and the inferred magnetic field orientations becoming more aligned with the major axis of the system. We quantitatively investigate these observational trends using a sample of protostars in the Perseus molecular cloud and compare these features with a non-ideal magnetohydrodynamic disc formation simulation. We find that the gas density increases faster than the magnetic field strength in the transition from the envelope to the disc scale, which makes it more difficult to magnetically align the grains on the disc scale. Specifically, to produce the observed ${\sim } 1{{\ \rm per\ cent}}$ polarization at ${\sim } 100\, \mathrm{au}$ scale via grains aligned with the B-field, even relatively small grains of $1\, \mathrm{\mu m}$ in size need to have their magnetic susceptibilities significantly enhanced (by a factor of ∼20) over the standard value, potentially through superparamagnetic inclusions. This requirement is more stringent for larger grains, with the enhancement factor increasing linearly with the grain size, reaching ∼2 × 104 for millimetre-sized grains. Even if the required enhancement can be achieved, the resulting inferred magnetic field orientation in the simulation does not show a preference for the major axis, which is inconsistent with the observed pattern. We thus conclude that the observed trends are best described by the model where the polarization on the envelope scale is dominated by magnetically aligned grains and that on the disc scale by scattering.

Constraining the Chemical Signatures and the Outburst Mechanism of the Class 0 Protostar HOPS 383

Abstract We present observations toward HOPS 383, the first known outbursting Class 0 protostar located within the Orion molecular cloud using the Atacama Large Millimeter/submillimeter Array (ALMA), Very Large Array (VLA), and Submillimeter Array (SMA). The SMA observations reveal envelope scale continuum and molecular line emission surrounding HOPS 383 at 0.85, 1.1, and 1.3 mm. The images show that HCO+ and H13CO+ peaks on or near the continuum, while N2H+ is reduced at the same position. This reflects the underlying chemistry where CO evaporating close to the protostar destroys N2H+ while forming HCO+. We also observe the molecular outflow traced by 12CO ( ) and ( ). A disk is resolved in the ALMA 0.87 mm dust continuum, orthogonal to the outflow direction, with an apparent radius of ∼62 au. Radiative transfer modeling of the continuum gives disk masses of 0.02 M ⊙ when fit to the ALMA visibilities. The models including VLA 8 mm data indicate that the disk mass could be up to a factor of 10 larger due to lower dust opacity at longer wavelengths. The disk temperature and surface density profiles from the modeling, and an assumed protostar mass of 0.5 M ⊙ suggest that the Toomre Q parameter < 1 before the outburst, making gravitational instability a viable mechanism to explain outbursts at an early age if the disk is sufficiently massive.

Transformable building envelope design in architectural education

Transformable building envelope design plays a key role in energy performance and sustainability of the built environment considering the thermal, lighting, acoustic, and visual comfort of the occupants, as well as aesthetics, economics and durability. Kinetic building envelopes may provide a real-time process of reconfiguration enlivening the environmental performance compared to conventional static building envelopes and enhancing the end-users’ comfort. Transformable systems may be developed for direct application on building façades, in order to provide control of natural lighting, ventilation and temperature of the inner spaces through their own surface configurations and materials. In architectural education, transformable building envelope design refers to an integrated approach of architectural development in terms of morphology, structure and construction. The methodology exposes students to the design logic of responsive systems as related with aspects of sustainability, materiality, functionality and aesthetics on one side and structure kinematics and stability on the other side. The pedagogical approach of respective projects conducted focuses on a nonlinear technology-driven design and analysis throughout different scales, from the element, to the system and building envelope scale. Primary aims of the projects presented in the current paper involve the conceptualization, investigation and analysis of kinetic mechanisms in physical models, geometrical simulations, motion analyses and daylight performance.

Indirect evidence of significant grain growth in young protostellar envelopes from polarized dust emission

ABSTRACT How and when in the star formation sequence do dust grains start to grow into pebbles is a cornerstone question to both star and planet formation. We compute the polarized radiative transfer from a model solar-type protostellar core, using the polaris code, aligning the dust grains with the local magnetic field, following the radiative torques (RATs) theory. We test the dependency of the resulting dust polarized emission with the maximum grain size of the dust size distribution at the envelope scale, from $a_\mathrm{max}=1\,$ to $50 \,\hbox{$\mu $m}$. Our work shows that, in the framework of RAT alignment, large dust grains are required to produce polarized dust emission at levels similar to those currently observed in solar-type protostellar envelopes at millimetre wavelengths. Considering the current theoretical difficulties to align a large fraction of small ISM-like grains in the conditions typical of protostellar envelopes, our results suggest that grain growth (typically $\gt 10 \,\hbox{$\mu $m}$) might have already significantly progressed at scales 100–1000 au in the youngest objects, observed less than 105 yr after the onset of collapse. Observations of dust polarized emission might open a new avenue to explore dust pristine properties and describe, for example, the initial conditions for the formation of planetesimals.

Influence of context-sensitive urban and architectural design factors on the energy demand of buildings in Toulouse, France

This research aims to identify the statistical sensitivity of multi-scale urban design factors regarding buildings’ energy demand located in three districts in the city of Toulouse, France. The research method is composed of four main steps: (a) three typical urban blocks of Toulouse are parametrized, considering factors ranging from the urban form to the building material scales; (b) a fractional factorial sampling method is applied which allows elaborating statistically representative and non-redundant scenarios from all design variables and for each specific urban district; (c) the urban energy models generated are interactively assessed regarding the annual buildings’ heating and cooling loads for the temperate climate context of Toulouse, France; (d) through a global sensitivity analysis, results obtained are estimated through a statistic hypothesis test, which allows identifying the influence of the design variables on each energy response of interest. Results show that urban multi-scale design variables may have divergent influence on the same energy response when the urban form context changes. For traditional urban compact blocks, two less current urban form factors considered in this study (the courtyard aspect ratio and the standard-deviation of the built height) account for almost 50% of the overall impact on heating demand of buildings while building and envelope scale factors, such as glazing window properties, have more influence for pavilions and slabs urban blocks. The relevance of certain factors was strongly linked to their typologies or to their urban environment.

The high rise building in the development of the chinese city. A research experience

The research activity started with the project for an international two step competition in China and was developed into an experimental research funded by the competition promoter. It has defined sustainable models, typologies and technologies for high-rise residential settlements in Chinese cities. The high-rise building and the technological implications, which affect the morphological structures, are the subject of study of influential research centres in the perspective of reducing energy consumption, through morphological control solutions and at the envelope scale. In this specific he definition of some technological systems, replicable in other application contexts, was a decisive element for the development of the research following the competition project.

Stellarator microinstabilities and turbulence at low magnetic shear

Gyrokinetic simulations of drift waves in low-magnetic-shear stellarators reveal that simulation domains comprised of multiple turns can be required to properly resolve critical mode structures important in saturation dynamics. Marginally stable eigenmodes important in saturation of ion temperature gradient modes and trapped electron modes in the Helically Symmetric Experiment (HSX) stellarator are observed to have two scales, with the envelope scale determined by the properties of the local magnetic shear and an inner scale determined by the interplay between the local shear and magnetic field-line curvature. Properly resolving these modes removes spurious growth rates that arise for extended modes in zero-magnetic-shear approximations, enabling use of a zero-magnetic-shear technique with smaller simulation domains and attendant cost savings. Analysis of subdominant modes in trapped electron mode (TEM)-driven turbulence reveals that the extended marginally stable modes play an important role in the nonlinear dynamics, and suggests that the properties induced by low magnetic shear may be exploited to provide another route for turbulence saturation.

A comparative Life Cycle Assessment of external wall-compositions for cleaner construction solutions in buildings

Application of Life Cycle Assessment (LCA) in buildings is usually performed at the envelope scale, mainly for comparison of several sample-solutions, and provides in-depth analyses of the related energy and environmental performances. In this way, it is possible to identify those solutions that perform best in energy and environmental terms, and that so are suitable for construction of sustainable buildings.In this context, the study was aimed at carrying out energy and environmental assessments to compare four external-wall samples characterised by different rates of sophistication in terms of assembly technologies and component materials.The samples considered were properly designed for development of the subsequent energy-environmental analysis. In particular, two “standard” wall compositions and two ventilated façades were considered, using rock-wool and recycled Polyethylene Terephthalate (R-PET) as insulating materials.The study documented that, as regards both energy and environmental impacts, ventilated façades perform quite well compared to the ”standard“ wall compositions, especially when equipped with R-PET. It also confirmed that both solutions easy to be disassembled and recycled materials are key design choices for environmental sustainable and low energy demanding buildings along their whole life cycles.Finally, the authors believe that the study provides helpful insights on the environmental sustainability of eco-friendly materials and technologies, and can contribute to less time and resources consuming LCAs at the building scale.

Magnetic field structure around cores with very low luminosity objects

[Abridged] We carried out optical polarimetry of five dense cores, (IRAM 04191, L1521F, L328, L673-7, and L1014) which are found to harbour VeLLO. This study was conducted mainly to understand the role played by the magnetic field in the formation of very low and substellar mass range objects using optical polarisation. The angular offsets between the envelope magnetic field direction (inferred from optical polarisation measurements) and the outflow position angles from the VeLLOs in IRAM 04191, L1521F, L328, L673-7, and L1014 are found to be 84$^\circ$, 53$^\circ$, 24$^\circ$, 08$^\circ$, and 15$^\circ$, respectively. The mean value of the offsets for all the five clouds is $\sim37^\circ$. If we exclude IRAM 04191, the mean value reduces to become $\sim25^\circ$. In IRAM 04191, the offset between the projected envelope and the inner magnetic field (inferred from the submillimetre data from SCUPOL) is found to be $\sim68^\circ$. The inner magnetic field, however, is found to be nearly aligned with the projected position angles of the minor axis, the rotation axis of the cloud, and the outflow from the IRAM 04191-IRS. We discuss a possible explanation for the nearly perpendicular orientation between the envelope and core scale magnetic fields in IRAM04191. The angular offset between the envelope magnetic field direction and the minor axis of IRAM 04191, L1521F, L673-7, and L1014 are 82$^\circ$, 60$^\circ$, 47$^\circ$, and 55$^\circ$, respectively. The mean value of the offsets between the envelope magnetic field and the minor axis position angles for the four cores is found to be $\sim60^\circ$. The results obtained from our study on the limited sample of five cores with VeLLOs show that the outflows in three of them tend to nearly align with the envelope magnetic field.

Matching fundamental and formant frequencies in vowels

In natural speech, there is a moderate correlation between fundamental frequency (F0) and formant frequencies (FF) associated with differences in larynx and vocal tract size across talkers. This study asks whether listeners prefer combinations of mean F0 and mean FF that mirror the covariation of these properties. The stimuli were vowel triplets (/i/-/a/-/u/) spoken by two men and two women and subsequently processed by Kawahara’s STRAIGHT vocoder. Experiment 1 included two continua, each containing 25 vowel triplets: one with the spectrum envelope (FF) scale factor fixed at 1.0 (i.e., unmodified) and F0 varied over ±2 oct, the other with F0 scale factor fixed at 1.0 and FF scale factors between 0.63 and 1.58. Listeners used a method of adjustment procedure to find the ‘‘best voice’’ in each set. For each continuum, best matches followed a unimodal distribution centered on the mean F0 or mean FF (F1, F2, F3) observed in measurements of vowels spoken by adult males and females. Experiment 2 showed comparable results when male vowels were scaled to the female range and vice versa. Overall the results suggest that listeners have an implicit awareness of the natural covariation of F0 and FF in human voices.

Nonlinear fluxes and forces from radio-frequency waves with application to driven flows in tokamaks

Nonlinear rf-driven sheared flows are of interest for turbulence control and basic physics experiments. Short-wavelength slow modes are required for efficient coupling of wave momentum to the plasma, requiring a kinetic hot-plasma theory. Here, a guiding-center formulation is developed which calculates the nonlinear particle and energy fluxes, energy absorption, and nonlinear forces on the plasma using a kinetic moment approach that is valid to first order in the ratio of the gyroradius compared to the wave envelope scale length and the plasma equilibrium scale length. Both the stress tensor and Lorentz force contribute to the net force on a fluid element. The forces driving flux-surface-averaged flows in a tokamak are extracted from the parallel and toroidal components. It is shown that flux-surface-averaged flows are driven by two classes of terms: direct absorption of wave momentum and dissipative stresses. Furthermore, the general kinetic expression for the force is shown to reduce to the standard cold-fluid ponderomotive force in an appropriate limit, but in this limit no flows are driven.

Exponential-algebraic transition in the near-field of low supersonic jets

The paper is concerned with the transition from exponential to algebraic cross-stream decay of instability waves in supersonic axisymmetric cold jets. The cross-stream structure of these waves is analysed for phase velocities close to the sound speed when the streamwise inhomogeneities of the mean flow are characterized by a small parameter. It is shown how algebraic decays are completely compatible with the features of the near-field, and a selection criterion for the occurence of such a behaviour is given. Near-field pressure fluctuations are then determined as functions of azimuthal properties of instability waves and control parameters. In some cases, where the dominant contribution to the sound generation is due to the axisymmetric Kelvin–Helmholtz instability mode, algebraic decays are not confined in the core region of the jet and the acoustic wavelength becomes larger than the envelope scale.

Effects of frequency shifts and visual gender information on vowel category judgments

Visual morphing techniques were used together with a high‐quality vocoder to study the audiovisual contribution of talker gender to the identification of frequency‐shifted vowels. A nine‐step continuum ranging from ‘‘bit’’ to ‘‘bet’’ was constructed from natural recorded syllables spoken by an adult female talker. Upward and downward frequency shifts in spectral envelope (scale factors of 0.85 and 1.0) were applied in combination with shifts in fundamental frequency, F0 (scale factors of 0.5 and 1.0). Downward frequency shifts generally resulted in malelike voices whereas upward shifts were perceived as femalelike. Two separate nine‐step visual continua from ‘‘bit’’ to ‘‘bet’’ were also constructed, one from a male face and the other a female face, each producing the end‐point words. Each step along the two visual continua was paired with the corresponding step on the acoustic continuum, creating natural audiovisual utterances. Category boundary shifts were found for both acoustic cues (F0 and formant fre...

Effects of frequency shifts on vowel category judgments

To investigate the effects of fundamental frequency (F0) and formant frequency shifts on vowel identification, a high-quality vocoder (‘‘STRAIGHT’’) was used to process the syllables ‘‘bit’’ and ‘‘bet’’ spoken by an adult female talker. From these two endpoints a nine-step continuum was generated by interpolation of the time-varying spectral envelope. Upward and downward frequency shifts in spectral envelope (scale factors of 0.75, 1.0, or 1.33) were combined with shifts in F0 (scale factors of 0.5, 1.0, or 1.25). Downward frequency shifts generally resulted in malelike voices whereas upward shifts were perceived as childlike. Matched frequency shifts, in which F0 and spectral envelope (i.e., formant frequencies) were shifted in the same direction, had relatively little effect on phoneme boundaries. Mismatched frequency shifts, in which F0 was modified independently of spectral envelope or vice versa, resulted in systematic boundary shifts. The changes in the identifications functions were qualitatively consistent with predictions of a model trained using acoustic measurements derived from a database of naturally spoken vowel tokens from men, women, and children. The empirical and modeling results are consistent with the idea that vowel boundary shifts are a consequence of listeners sensitivity to the statistical structure of natural speech.

Intelligibility of frequency-shifted speech

A significant fact about speech perception is that intelligibility can be preserved when the formant pattern is shifted up or down along the frequency scale. To study the relationship between fundamental frequency (F0) and spectrum envelope shifts, we used a high-quality vocoder (‘‘Straight’’) to process a set of 280 English sentences from the Hearing in Noise Test. Upward shifts in spectrum envelope (shift factors of 1, 2, 3, or 4) were combined with upward shifts in F0 (shift factors of 1, 2, or 4). Word recognition accuracy dropped from near perfect for a spectrum envelope shift factor of 1 (unshifted speech) to 77%, 24%, and 7% for shift factors of 2, 3, and 4, respectively. F0 shifts had a small but significant effect on identification. For a spectrum envelope scale factor of 1, increasing F0 by two octaves (shift factor of 4) resulted in a 16% decline. However, for spectrum envelope shift factors of 2 or greater, increasing F0 led to an improvement in performance. The results are consistent with the hypothesis that learned relationships between F0 and spectrum envelope affect the intelligibility of frequency-shifted speech.

The effects of blur and size on monocular and stereoscopic localization

Monocular localization of non-abutting stimuli and stereoscopic localization of the same second-order targets are performed with the same precision (Wilcox, L.M. & Hess, R.F. (1996) Is the site of non-linear filtering in stereopsis before or after binocular combination? Vision Research, 36, 391–399). Further, both tasks show a similar dependence on the scale of the stimulus. Since prior studies used Gaussian-enveloped stimuli, modifications of stimulus scale produced concurrent changes in edge blur. The experiments reported here assess the relative contributions of size and blur to the observed dependence on envelope scale for both monocular localization and stereoacuity. Stereoacuity for first-order targets was found to be an order of magnitude better than stereoacuity for second-order targets and monocular acuity for both first- and second-order targets. Further, while first-order stereopsis was found to depend solely on blur, second-order stereoacuity and monocular acuity were affected by both size and blur. These results suggest that while stereoacuity for first-order stimuli may be determined by a correlative process limited by early additive noise, stereoacuity for second-order stimuli and monocular acuity for non-abutting targets are more likely limited by stimulus-dependent spatial subsampling.