El modelado de las laderas del cañón de Casla (Segovia): los abrigos o balmas y su significado geomorfológico

[Resumen] Se describe la morfología de las laderas del cañón de Casla (provincia de Segovia), cuya principal característica es la presencia de varios niveles de abrigos o balmas, adquiriendo las laderas una forma típica en una sucesión de escarpes sobreexcavados o vertientes en extraplomo (flared slopes). La génesis de los abrigos se ha relacionado con las fases de encajamiento del río Caslilla (afluente del Duratón): en los momentos de acumulación o estabilización fluvial se produciría una erosión subsuperficial preferentemente al pie de cada escarpe en contacto con el suelo, desarrollándose estas formas, mientras que en las fases de incisión del río quedarían expuestas y colgadas respecto al nuevo nivel de base del río[Abstract] This paper explains the several fIares (rock shelters) levels on Casla canyon slopes. Each flare is related to a stabilization period of Caslilla river. During this period, a lateral subsurface weathering erosion formed the fIare leve!. Afterwards, with the new incision of the river, the fIare level remained hanging. The succession of different periods of stabilization and incision of the river is interpreted as the origin of these flared slopes

Transformación y progresiva integración de un municipio de montaña: Prádena de la Sierra, Guadarrama oriental (Segovia)

Sin resume

Assessment of load alleviation in aircraft due to structural flexibility

An evaluation of the effect of structural flexibility in aircraft loads is presented. The assessment is performed for two flight conditions: cruise and vertical gust encounter. These conditions are determined by several parameters, some of them based on actual certiffication regulations. To determine the effect of structural flexibility an aeroelastic model is developed: aerodynamic loads are obtained by a 3D numerical panel method based on vortex ring and horseshoe elements developed with Matlab [25], and structural deformation caused by external loads in a flexible structure is computed with ANSYS FEM software [3]. The model analysed is designed based on its aeroelastic modal frequencies. Different configurations of the wing are evaluated to determine the most relevant parameters involved in load alleviation. With the aim of updating the FEM model, a scaled specimen and a proper GVT are defined to obtain the real modal frequencies of the structure in future works and to use the experimental setup for teaching purposes at the university.Ingeniería Aeroespacia

Observational studies of a dense cloud core on the verge of star formation

Pre-stellar cores represent the first identifiable stages of star formation, and are therefore perfect laboratories for astronomers to study how our own Solar system was formed. This thesis focuses on L1544, a pre-stellar core situated in the nearby Taurus Molecular Cloud, at a distance of 140 pc from us. The proximity allows us to resolve the inner structure of the core with currently available telescopes, and to zoom in on the inner, very dense regions. The core shows clear signs of contraction and chemical evolution, and its nucleus is very dense (n(H2) > 10^7 cm−3) and cold (T < 7 K). The physical structure of L1544 has been recently modeled, and this model agrees well with the observed molecular line and continuum emission. Moreover, the model predicts an increase in the dust opacity by a factor of 4 towards the central regions of L1544, which suggests grain coagulation towards the center. This theory can only be tested studying the continuum emission at millimeter wavelengths, as this is the spectral window expected to be affected by emission from large grains. Currently it is not known if grain coagulation is effective already during the prestellar phase, before the formation of a protostar. Studying this effect is important, as dust coagulation can affect the formation and evolution of protoplanetary disks. In this thesis, I present studies of dust emission properties and physical and chemical conditions in the pre-stellar core L1544. These studies are based on continuum and spectral line observations at millimeter wavelengths. The continuum observations with the IRAM 30 m telescope, presented in the first part of this thesis, can be modeled with a constant value of the dust opacity and spectral index, with no indication of grain growth in this core. It is shown, however, that the spatial resolution and the sensitivity of the observations are not sufficient for detecting the predicted effect, but interferometers, such as ALMA, should be able to find evidence for grain growth in the inner 2000 au of the core. The second part of this thesis discusses deuterated methanol (CH2DOH), a molecule which is solely formed on the dust grain surfaces, and its relation to CO, H2CO, and their isotopologues. The formation of CH2DOH requires large amounts of CO on grains, so it is useful to study both molecules simultaneously. Comparison with H2CO, which can also form in the gas, helps to understand the different conditions governing gas-phase and solid-phase reactions. As expected, we find that CH2DOH and methanol (CH3OH) thrive in similar conditions, and that both species form where CO is sufficiently depleted. On the other hand, H2CO and its deuterated species show different distributions than those of CH3OH, CH2DOH, and C17O, indicating that gas-phase reactions may play an important role. Comparison between two different chemical models shows that theoretical calculations should take into account reactive desorption, quantum tunneling, and time evolution. A need for further laboratory work is also pointed out. The last part of the thesis focuses on the dust continuum emission from L1544 at 1.1 and 3.3 mm. These new maps, obtained with two of the newest mm-continuum facilities (AzTEC at the LMT and MUSTANG-2 at the GBO) show gradients in the dust opacity across the cloud, which is consistent with variations in the thickness of the ice mantles on the dust grains surfaces. Our results also show that the current physical description of the cloud needs to be revised

Plasma basic concepts and nitrogen containing plasmas

Basic concepts related to plasmas are described as well as the typical characterization methods currently available. A brief overview about some plasma applications is given, but focusing on plasma used in material processing mainly devoted to the microelectronics industry. Finally, specific applications related to plasma-assisted MBE for nitrides and dilute nitrides are given, showing some interesting research works performed to that purpose, and giving the usual characterization techniques commonly used in such processes

A study of the cc-C3HD\mathrm{C_{3}HD}/cc-C3H2\mathrm{C_{3}H_{2}} ratio in low-mass star forming regions

We use the deuteration of $c$-$\mathrm{C_{3}H_{2}}$ to probe the physical parameters of starless and protostellar cores, related to their evolutionary states, and compare it to the $\mathrm{N_{2}H^{+}}$-deuteration in order to study possible differences between the deuteration of C- and N-bearing species. We observed the main species $c$-$\mathrm{C_{3}H_{2}}$, the singly and doubly deuterated species $c$-$\mathrm{C_{3}HD}$ and $c$-$\mathrm{C_{3}D_{2}}$, as well as the isotopologue $c$-$\mathrm{{H^{13}CC_{2}H}}$ toward 10 starless cores and 5 protostars in the Taurus and Perseus Complexes. We examined the correlation between the $N$($c$-$\mathrm{C_{3}HD}$)/$N$($c$-$\mathrm{C_{3}H_{2}}$) ratio and the dust temperature along with the $\mathrm{H_2}$ column density and the CO depletion factor. The resulting $N$($c$-$\mathrm{C_{3}HD}$)/$N$($c$-$\mathrm{C_{3}H_{2}}$) ratio is within the error bars consistent with $10\%$ in all starless cores with detected $c$-$\mathrm{C_{3}HD}$. This also accounts for the protostars except for the source HH211, where we measure a high deuteration level of $23\%$. The deuteration of $\mathrm{N_{2}H^{+}}$ follows the same trend but is considerably higher in the dynamically evolved core L1544. Toward the protostellar cores the coolest objects show the largest deuterium fraction in $c$-$\mathrm{C_{3}H_{2}}$. We show that the deuteration of $c$-$\mathrm{C_{3}H_{2}}$ can trace the early phases of star formation and is comparable to that of $\mathrm{N_{2}H^{+}}$. However, the largest $c$-$\mathrm{C_{3}H_{2}}$ deuteration level is found toward protostellar cores, suggesting that while $c$-$\mathrm{C_{3}H_{2}}$ is mainly frozen onto dust grains in the central regions of starless cores, active deuteration is taking place on ice

Search for grain growth towards the center of L1544

In dense and cold molecular clouds dust grains are surrounded by thick icy mantles. It is however not clear if dust growth and coagulation take place before the switch-on of a protostar. This is an important issue, as the presence of large grains may affect the chemical structure of dense cloud cores, including the dynamically important ionization fraction, and the future evolution of solids in protoplanetary disks. To study this further, we focus on L1544, one of the most centrally concentrated pre-stellar cores on the verge of star formation, and with a well-known physical structure. We observed L1544 at 1.2 and 2 mm using NIKA, a new receiver at the IRAM 30 m telescope, and we used data from the Herschel Space Observatory archive. We find no evidence of grain growth towards the center of L1544 at the available angular resolution. Therefore, we conclude that single dish observations do not allow us to investigate grain growth toward the pre-stellar core L1544 and high sensitivity interferometer observations are needed. We predict that dust grains can grow to 200 $\mu$m in size toward the central ~300 au of L1544. This will imply a dust opacity change by a factor of ~2.5 at 1.2 mm, which can be detected using the Atacama Large Millimeter and submillimeter Array (ALMA) at different wavelengths and with an angular resolution of 2".Comment: 12 pages, 14 figures. Accepted for publication in A&

Improved determination of the 1(0)-0(0) rotational frequency of NH3D+ from the high resolution spectrum of the v4 infrared band

The high resolution spectrum of the v4 band of NH3D+ has been measured by difference frequency IR laser spectroscopy in a multipass hollow cathode discharge cell. From the set of molecular constants obtained from the analysis of the spectrum, a value of 262817(6) MHz (3sigma) has been derived for the frequency of the 1(0)-0(0) rotational transition. This value supports the assignment to NH3D+ of lines at 262816.7 MHz recorded in radio astronomy observations in Orion-IRc2 and the cold prestellar core B1-bS.Comment: Accepted for publication in the Astrophysical Journal Letters 04 June 201

New accurate measurement of 36ArH+ and 38ArH+ ro-vibrational transitions by high resolution IR absorption spectroscopy

The protonated Argon ion, $^{36}$ArH$^{+}$, has been identified recently in the Crab Nebula (Barlow et al. 2013) from Herschel spectra. Given the atmospheric opacity at the frequency of its $J$=1-0 and $J$=2-1 rotational transitions (617.5 and 1234.6 GHz, respectively), and the current lack of appropriate space observatories after the recent end of the Herschel mission, future studies on this molecule will rely on mid-infrared observations. We report on accurate wavenumber measurements of $^{36}$ArH$^{+}$ and $^{38}$ArH$^{+}$ rotation-vibration transitions in the $v$=1-0 band in the range 4.1-3.7 $\mu$m (2450-2715 cm$^{-1}$). The wavenumbers of the $R$(0) transitions of the $v$=1-0 band are 2612.50135$\pm$0.00033 and 2610.70177$\pm$0.00042 cm$^{-1}$ ($\pm3\sigma$) for $^{36}$ArH$^{+}$ and $^{38}$ArH$^{+}$, respectively. The calculated opacity for a gas thermalized at a temperature of 100 K and a linewidth of 1 km.s$^{-1}$ of the $R$(0) line is $1.6\times10^{-15}\times N$($^{36}$ArH$^+$). For column densities of $^{36}$ArH$^+$ larger than $1\times 10^{13}$ cm$^{-2}$, significant absorption by the $R$(0) line can be expected against bright mid-IR sources