Quantum Interference in Single Molecule Electronic Systems

We present a general analytical formula and an ab initio study of quantum interference in multi-branch molecules. Ab initio calculations are used to investigate quantum interference in a benzene-1,2-dithiolate (BDT) molecule sandwiched between gold electrodes and through oligoynes of various lengths. We show that when a point charge is located in the plane of a BDT molecule and its position varied, the electrical conductance exhibits a clear interference effect, whereas when the charge approaches a BDT molecule along a line normal to the plane of the molecule and passing through the centre of the phenyl ring, interference effects are negligible. In the case of olygoynes, quantum interference leads to the appearance of a critical energy $E_c$, at which the electron transmission coefficient $T(E)$ of chains with even or odd numbers of atoms is independent of length. To illustrate the underlying physics, we derive a general analytical formula for electron transport through multi-branch structures and demonstrate the versatility of the formula by comparing it with the above ab-initio simulations. We also employ the analytical formula to investigate the current inside the molecule and demonstrate that large counter currents can occur within a ring-like molecule such as BDT, when the point charge is located in the plane of the molecule. The formula can be used to describe quantum interference and Fano resonances in structures with branches containing arbitrary elastic scattering regions connected to nodal sites.Comment: 12 pages, 11 figure

Drag reduction on a blunt body by self-adaption of rear flexibly hinged flaps

We study the aerodynamics of a blunt-based body with rear flexibly-hinged rigid flaps, subject to a turbulent flow of Reynolds number Re = 12000, under aligned and cross flow conditions with yaw angle β = 0◦ and β = 4◦. To that aim, different values of the equivalent torsional stiffness are considered, to cover the range of reduced velocity U∗ = (0, 3.48] in water tank experiments. The effect of the angular deflection of plates on the drag and near wake flow is analyzed, experimentally and numerically. The results show that, in the range of U∗ herein considered, the plates undergo an inwards quasi-static, self-adaptive deflection, which is symmetric for yaw angles β = 0◦ and asymmetric for β = 4◦. In particular, the plates feature small mean deformation angles for values of U∗ < 1, whereas a sharp and monotonic increase of such deflection occurs for U∗ > 1, i.e. for lower values of the hinge’s stiffness, with an asymptotic trend towards the larger values of U∗. A critical value of reduced velocity of U∗ ≃ 0.96 is obtained as the instability threshold above which plates depart from their initial equilibrium position. The progressive streamlining of the trailing edge translates into significant reductions of the associated mean drag coefficients. Thus, reductions close to 19% with respect to reference static plates configurations are obtained for the most flexible case of U∗ = 3.48 for both β = 0◦ and β = 4◦. A close inspection of the near wake reveals that the inwards progressive mean displacement of the plates yields a reduction in the recirculation bubble size. A symmetric evolution of the recirculating bubble is observed for β = 0◦, whereas the bubble becomes asymmetric for β = 4◦, with a larger leeward clockwise vortex. In both cases, the drag coefficient is shown to vary linearly with the global aspect ratio of the recirculating bubble. The analysis of the numerical results shows that the reduced extension of the recirculating bubble significantly alters the formation length and intensity of the eddies size and associated pressure. It is observed that despite the local pressure decrease in the vortices shed from the trailing edges, the plates self adaption reduces their size and prevents the eddies from entering the cavity, thus, creating a dead flow region with a consequent pressure increase at the body base.Junta de Andalucia FEDER-UJA 1262764Universidad de JaenEuropean CommissionSpanish MCIN/AEI PDC2021-121288-I00European Union Next Generation EU/PRT

PENGARUH MEDIA PEMBELAJARAN MIND MAPPING TERHADAP MINAT BELAJAR PESERTA DIDIK PADA PELAJARAN EKONOMI KELAS XI IPS 1 di SMA NEGERI 27 BANDUNG

Judul penelitian ini adalah pengaruh media pembelajaran mind mapping terhadap minat belajar peserta didik pada pelajaran ekonomi kelas XI IPS 1 di SMA Negeri 27 Bandung tahun ajaran 2016-2017. Berdasarkan tinjauan langsung di SMA Negeri 27 Bandung kelas XI IPS 1, Pembelajaran konvensional (ceramah) hanya membuat peserta didik kurang aktif dan malas dalam menerima materi yang ada, karena pembelajaran hanya terpusat pada apa yang disampaikan sehingga tidak dapat dimengerti secara maksimal. Tujuan dari penelitian ini adalah: (1) Mengetahui penggunaan media mind mapping pada mata pelajaran ekonomi kelas XI IPS 1 di SMA Negeri 27 Bandung. (2) Mengetahui minat belajar peserta didik pada mata pelajaran ekonomi kelas XI IPS 1 di SMA Negeri 27 Bandung. (3) Mengetahui seberapa besar pengaruh media mind mapping terhadap minat belajar peserta didik pada mata pelajaran ekonomi kelas XI IPS 1 di SMA Negeri 27 Bandung. Metode yang digunakan dalam penelitian ini adalah survei. Teknik pengumpulan data yang digunakan yaitu observasi dan angket dengan teknik pengolahan data uji validitas, uji reliabilitas, uji normalitas data, analisis regresi linier sederhana dan koefisien determinasi, Hipotesis penelitian berbunyi “Terdapat pengaruh antara media pembelajaran mind mapping (X) terhadap minat belajar peserta didik (Y) pada mata pelajaran ekonomi. Hasil penelitian ini adalah terdapat pengaruh antara variabel X dan Variabel Y sebesar 0,336 atau 33,60%. Untuk mengetahui hubungan fungsional antara variabel X dan variabel Y maka digunakan analisis regresi linier sederhana dengan hasil perhitungan sebagai berikut : Y = 9.915 + 0.537 X artinya bahwa setiap media pembelajaran mind mapping bertambah 9,915 maka minat belajar meningkat sebesar 0,537. Untuk mengetahui seberapa besar pengaruh variabel X (media pembelajaran mind mapping) terhadap variabel Y (minat belajar), maka digunakan koefisien determinasi dengan hasil perhitungan sebesar 33,60% maka sebagian lainnya ditentukan oleh faktor lain yang tidak diteliti. Kesimpulan hipotesis penelitian dapat diterima, sebagai akhir penelitian penulis menyampaikan saran kepada guru agar sebaiknya guru menggunakan variasi media pembelajaran yang menarik berkaitan dengan materi pelajaran yang akan disampaikan, karena cara ini dapat membuat peserta didik aktif dan kreatif untuk belajar. Kepada para praktisi atau peneliti lain di bidang pendidikan dapat melakukan penelitian serupa dengan media pembelajaran dan metode yang berbeda agar diperoleh berbagai alternatif untuk peningkatan pemahaman pembelajaran pada pokok bahasan selanjutnya dan kepada pihak sekolah sebagai bahan kajian bagi sekolah dan menyarankan guru untuk menggunakan media pembelajaran yang mampu meningkatkan prestasi belajar peserta didik untuk mendukung pendekatan saintifik dan media pembelajaran yang baik. Kata Kunci : media pembelajaran mind mapping, minat Belajar

Contribution of mangotoxin to the virulence and epiphytic fitness of Pseudomonas syringae pv. syringae

Mangotoxin is an antimetabolite toxin that inhibits ornithine acetyl transferase, a key enzyme in the biosynthetic pathway of ornithine and arginine and recently reported in strains of Pseudomonas syringae pv. syringae (Pss) isolated from mango. Since symptoms on mango tissues are very difficult to reproduce, in this study the role of mangotoxin in Pss virulence was addressed by analyzing the in planta growth and development of disease symptoms on tomato leaflets. Inoculation experiments were carried out following several procedures using the wild-type strain Pss UMAF0158, two Tn5-mutant derivative strains defective in mangotoxin production, and their complemented derivative strains in which mangotoxin production is restored. The ability of the mangotoxin-defective mutants to grow in planta was similar, and their epiphytic survival on the tomato leaf surface identical to the wild-type and complemented strains. However, both the disease index data of incidence and the severity of necrotic symptoms indicated that mangotoxin-defective mutants were less virulent, indicating that mangotoxin is a virulence factor. Furthermore, competition experiments showed that the survival values of the wild-type strain were slightly but significantly higher than those of the mangotoxin-defective mutants, suggesting that mangotoxin production would improve the epiphytic fitness of Pss. [Int Microbiol 2009; 12(2):87-95

The Possible White Dwarf-Neutron Star Connection

The current status of the problem of whether neutron stars can form, in close binary systems, by accretion-induced collapse (AIC) of white dwarfs is examined. We find that, in principle, both initially cold C+O white dwarfs in the high-mass tail of their mass distribution in binaries and O+Ne+Mg white dwarfs can produce neutron stars. Which fractions of neutron stars in different types of binaries (or descendants from binaries) might originate from this process remains uncertain.Comment: 6 pages. To appear in "White Dwarfs", ed. J. Isern, M. Hernanz, and E. Garcia-Berro (Dordrecht: Kluwer

Finite axisymmetric charged dust disks in conformastatic spacetimes

An infinite family of axisymmetric charged dust disks of finite extension is presented. The disks are obtained by solving the vacuum Einstein-Maxwell equations for conformastatic spacetimes, which are characterized by only one metric function. In order to obtain the solutions, it is assumed that the metric function and the electric potential are functionally related and that the metric function is functionally dependent of another auxiliary function, which is taken as a solution of Laplace equation. The solutions for the auxiliary function are then taken as given by the infinite family of generalized Kalnajs disks recently obtained by Gonz\'alez and Reina (MNRAS 371, 1873, 2006), which is expressed in terms of the oblate spheroidal coordinates and represents a well behaved family of finite axisymmetric flat galaxy models. The so obtained relativistic thin disks have then a charge density that is equal, except maybe by a sign, to their mass density, in such a way that the electric and gravitational forces are in exact balance. The energy density of the disks is everywhere positive and well behaved, vanishing at the edge. Accordingly, as the disks are made of dust, their energy-momentum tensor it agrees with all the energy conditions.Comment: Submitted to PR