The “question of the technique”: from the designing idea to the realized form

This work aims at focusing the inner relationship between the formal intuition of the design process and the structural/technological boundaries behind the creation of any architectural constructed form. Through the analysis of some noteworthy architectural examples, we highlight the reasons for which their designers achieved a virtuous equilibrium between shape, design and constructive awareness. In a contemporary era in which the major architectural production seems more interested to show off and amaze the spectators with huge scales and charming contaminations from the entertainment industry, a call for the need of the Vitruvian lesson appears essentials: the more we push our creativity as designers, the more we need to keep it firmly stick to the principles of firmitas, utilitas and venusta

Open clusters: III. Fundamental parameters of B stars in NGC 6087, NGC 6250, NGC 6383 and NGC 6530. B type stars with circumstellar envelopes

Context. Stellar physical properties of star clusters are poorly known. Aims. Our goals are to perform a spectrophotometric study of the B star population in open clusters to derive accurate stellar parameters, search for the presence of circumstellar envelopes, and discuss the characteristics of these stars. Methods. The BCD spectrophotometric system is a powerful tool to obtain fundamental parameters and infer the main properties of open clusters: distance modulus, color excess, and age. We inspected the Balmer discontinuity to seek circumstellar disks and identify Be-star candidates. High resolution spectra in the H$\alpha$ region are used to confirm the Be nature. Results. We provide Teff , log g, Mv , Mbol and spectral types for a sample of 68 stars in the field of the open clusters NGC 6087, NGC 6250, NGC 6383, and NGC 6530, as well as the cluster distances, ages and reddening. Then, based on a sample of 230 B stars in the direction of the 11 open clusters studied along this series of three papers, we report 6 new Be stars, 4 blue straggler candidates, and 15 B-type stars (called Bdd) with a double Balmer discontinuity. We also find that the majority of the Be stars are dwarfs and present a maximum at the spectral type B2-B4 in young and intermediate-age open clusters. Another maximum of Be stars is observed at the spectral type B6-B8 in open clusters older than 40 Myr, where the population of Bdd stars also becomes relevant. Conclusions. Our results support previous statements that the Be phenomenon is present along the whole main sequence band and occurs in very different evolutionary states. We find clear evidence of an increase of stars with circumstellar envelopes with cluster age. The Be phenomenon reaches its maximum in clusters of intermediate age and the number of B stars with circumstellar envelopes (Be+Bdd stars) is also high for the older clusters

Full evolution of low-mass white dwarfs with helium and oxygen cores

We study the full evolution of low-mass white dwarfs with helium and oxygen cores. We revisit the age dichotomy observed in many white dwarf companions to millisecond pulsar on the basis of white dwarf configurations derived from binary evolution computations. We evolve 11 dwarf sequences for helium cores with final masses of 0.1604, 0.1869, 0.2026, 0.2495, 0.3056, 0.3333, 0.3515, 0.3844, 0.3986, 0.4160 and 0.4481 M. In addition, we compute the evolution of five sequences for oxygen cores with final masses of 0.3515, 0.3844, 0.3986, 0.4160 and 0.4481 M. A metallicity of Z = 0.02 is assumed. Gravitational settling, chemical and thermal diffusion are accounted for during the white dwarf regime. Our study reinforces the result that diffusion processes are a key ingredient in explaining the observed age and envelope dichotomy in low-mass helium-core white dwarfs, a conclusion we arrived at earlier on the basis of a simplified treatment for the binary evolution of progenitor stars. We determine the mass threshold where the age dichotomy occurs. For the oxygen white dwarf sequences, we report the occurrence of diffusion-induced, hydrogen-shell flashes, which, as in the case of their helium counterparts, strongly influence the late stages of white dwarf cooling. Finally, we presensent our results as a set of white dwarf mass–radius relations for helium and oxygen cores.Fil: Panei, Jorge Alejandro. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Althaus, Leandro Gabriel. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - La Plata. Instituto de Astrofísica La Plata. Universidad Nacional de La Plata. Facultad de Ciencias Astronómicas y Geofísicas. Instituto de Astrofísica La Plata; ArgentinaFil: Chen, X.. Chinese Academy of Sciences; República de ChinaFil: Han, Z.. Chinese Academy of Sciences; República de Chin

Evolution of iron core white dwarfs

Recent measurements made by Hipparcos (Provencal et al. 1998) present observational evidence supporting the existence of some white dwarf (WD) stars with iron - rich, core composition. In this connection, the present paper is aimed at exploring the structure and evolution of iron - core WDs by means of a detailed and updated evolutionary code. In particular, we examine the evolution of the central conditions, neutrino luminosity, surface gravity, crystallization, internal luminosity profiles and ages. We find that the evolution of iron - rich WDs is markedly different from that of their carbon - oxygen counterparts. In particular, cooling is strongly accelerated as compared with the standard case. Thus, if iron WDs were very numerous, some of them would have had time enough to evolve at lower luminosities than that corresponding to the fall - off in the observed WD luminosity function.Comment: 8 pages, 21 figures. Accepted for publication in MNRA

A deep and wide-field view at the IC 2944 / 2948 complex in Centaurus

We employed the ESO MPI wide-field camera and obtained deep images in the VIc pass-bands in the region of the IC 2944/2948 complex (l ~ 294; b ~ -1), and complemented them with literature and archival data. We used this material to derive the photometric, spectroscopic and kinematic properties of the brightest (V < 16) stars in the region. The VI deep photometry on the other end, helped us to unravel the lower main sequence of a few, possibly physical, star groups in the area. Our analysis confirmed previous suggestions that the extinction toward this line of sight follows the normal law (Rv = 3.1). We could recognize B-type stars spread in distance from a few hundred pc to at least 2 kpc. We found two young groups (age ~ 3 Myr) located respectively at about 2.3 and 3.2 kpc from the Sun. They are characterized by a significant variable extinction (E(B-V) ranging from 0.28 to 0.45 mag), and host a significant pre-main sequence population. We computed the initial mass functions for these groups and obtained slopes Gamma from -0.94 to -1.02 (e_Gamma = 0.3), in a scale where the classical Salpeter law is -1.35. We estimated the total mass of both main stellar groups in ~ 1100$and ~ 500$ Mo, respectively. Our kinematic analysis indicated that both groups of stars deviate from the standard rotation curve of the Milky Way, in line with literature results for this specific Galactic direction. Finally, along the same line of sight we identified a third group of early-type stars located at ~ 8 kpc from the Sun. This group might be located in the far side of the Sagittarius-Carina spiral arm.Comment: 13 pages, 11 figures, accepted for publication in MNRA

Final Evolution and Delayed Explosions of Spinning White Dwarfs in Single Degenerate Models for Type Ia Supernovae

We study the occurrence of delayed SNe~Ia in the single degenerate (SD) scenario. We assume that a massive carbon-oxygen (CO) white dwarf (WD) accretes matter coming from a companion star, making it to spin at the critical rate. We assume uniform rotation due to magnetic field coupling. The carbon ignition mass for non-rotating WDs is M_{ig}^{NR} \approx 1.38 M_{\odot}; while for the case of uniformly rotating WDs it is a few percent larger (M_{ig}^{R} \approx 1.43 M_{\odot}). When accretion rate decreases, the WD begins to lose angular momentum, shrinks, and spins up; however, it does not overflow its critical rotation rate, avoiding mass shedding. Thus, angular momentum losses can lead the CO WD interior to compression and carbon ignition, which would induce an SN~Ia. The delay, largely due to the angular momentum losses timescale, may be large enough to allow the companion star to evolve to a He WD, becoming undetectable at the moment of explosion. This scenario supports the occurrence of delayed SNe~Ia if the final CO WD mass is 1.38 M_{\odot} < M < 1.43 M_{\odot}. We also find that if the delay is longer than ~3 Gyr, the WD would become too cold to explode, rather undergoing collapse.Comment: 6 pages, 5 figures, published in the Astrophysical Journal Letters, 809, L6 (2015), added some corrections for errat

The progenitor of binary millisecond radio pulsar PSR J1713+0747

Context. PSR J1713+0747 is a binary system comprising millisecond radio pulsar with a spin period of 4.57 ms, and a low-mass white dwarf (WD) companion orbiting the pulsar with a period of 67.8 days. Using the general relativistic Shapiro delay, the masses of the WD and pulsar components were previously found to be 0.28 ± 0.03 M⊙ and 1.3 ± 0.2 M ⊙ (68% confidence), respectively. Aims. Standard binary evolution theory suggests that PSR J1713+0747 evolved from a low-mass X-ray binary (LMXB). Here, we test this hypothesis. Methods. We used a binary evolution code and a WD evolution code to calculate evolutionary sequences of LMXBs that could result in binary millisecond radio pulsars such as PSR J1713+0747. Results. During the mass exchange, the mass transfer is nonconservative. Because of the thermal and viscous instabilities developing in the accretion disk, the neutron star accretes only a small part of the incoming material. We find that the progenitor of PSR J1713+0747 can be modelled as an LMXB including a donor star with mass 1.3 - 1.6 M⊙ and an initial orbital period ranging from 2.40 to 4.15 days. If the cooling timescale of the WD is 8 Gyr, its present effective temperature is between 3870 and 4120 K, slightly higher than the observed value. We estimate a surface gravity of Log(g) ≈ 7.38 - 7.40.Facultad de Ciencias Astronómicas y Geofísica

Pengaruh produk dan promosi terhadap keputusan nasabah memilih tabungan emas pada PT. Pegadaian (Persero) Unit Pelayanan Syariaha Sipirok

Permasalahan dalam penelitian ini dilatarbelakangi oleh nasabah pegadaian syariah yang menggunakan produk tabungan emas tidak sesuai dengan target perusahaan dalam mendapatkan nasabah. Hal ini disebabkan karena produk tabungan emas merupakan produk yang belum diketahui banyak oleh nasabah PT. Pegadaian (Persero) Unit Pelayanan Syariah Sipirok. Rumusan masalah dalam penelitian ini adalah apakah produk dan promosi memiliki pengaruh signifikan terhadap keputusan nasabah memilih tabungan emas baik secara parsial dan simultan. Tujuan penelitian ini adalah untuk mengetahui apakah produk dan promosi memiliki pengaruh signifikan terhadap keputusan nasabah memilih tabungan emas pada PT. Pegadaian (Persero) Unit Pelayanan Syariah Sipirok. Teori yang digunakan dalam penelitian ini adalah teori tentang keputusan nasabah yang terdiri dari pengertian pengambilan keputusan, proses pengambilan keputusan, tingkat masalah dalam pengambilan keputusan. Selanjutnya teori tentang produk yang terdiri dari pengertian produk, klasifikasi produk yang terdiri dari harga, variasi produk, dan kualitas produk, dan terakhir teori promosi yang terdiri dari pengertian promosi, promosi melalui iklan, pemasaran langsung, dan pemasaran interaktif. Penelitian ini merupakan penelitian kuantitatif dengan menggunakan analisis regresi linier berganda. Teknik pengumpulan data menggunakan kuisioner dengan sampel 42 nasabah. Pengolahan data dilakukan dengan SPSS versi 22. Hasil penelitian ini menunjukkan secara parsial faktor produk tidak memiliki pengaruh terhadap keputusan nasabah memilih tabungan emas dengan nilai thitung ttabel (2,622 > 2,022). Berdasarkan hasil uji secara simultan bahwa factor produk dan factor promosi memiliki pengaruh terhadap keputusan nasabah memili tabungan emas dengan nilai Fhitung > Ftabel (3,439 > 3,24). Berdasarkan hasil uji koefisien determinasi dapat diketahui bahwa 15% variabel produk dan promosi mampu mempengaruhi keputusan nasabah memilih tabungan emas dan 85% sisanya dipengaruhi oleh variabel lain yang tidak dibahas dalam penelitian in

The tuffs of the “Servian Wall” in Rome

In the context of the current scientific collaboration between the Soprintendenza per i Beni Archeologici di Roma and the Laboratorio di Sperimentazione Mineraria e Petrografica del Ministero dello Sviluppo Economico, a study has been carried out on some tuff blocks recovered during the redecoration of the historic building where our laboratory is located (the building is on Quirinale hill). Archaeological sources affirm that these blocks belong to the first wall that surrounded Rome, the wall named “Mura Serviane”. It was built from the 6th to the 4th century B.C. An archaeometric study of the tuff blocks has been carried out aiming to identify the kind of raw materials used and to compare the results with the data regarding the tuff banks set in the area of Rome: in the central area and in the north of Rome.Au cours de la collaboration scientifique entreprise avec la Soprintendenza per i Beni Archeologici di Roma, nous avons étudié des blocs de tuf trouvés pendant les travaux pour la restauration du bâtiment où se trouve notre laboratoire; le bâtiment se trouve sur la colline du Quirinal. Les sources archéologiques affirment que ces blocs appartiennent à la première muraille, « Mura Serviane », qui protégeaient la cité de Rome; ces murs ont été construits du sixième au quatrième siècle avant Jésus Christ. Le but de cette étude est l’identifier le matériau utilisé et de rechercher des carrières desquelles ces blocs ont été prélevés