9,745 research outputs found
Non-Tachyonic Semi-Realistic Non-Supersymmetric Heterotic String Vacua
The heterotic--string models in the free fermionic formulation gave rise to
some of the most realistic string models to date, which possess N=1 spacetime
supersymmetry. Lack of evidence for supersymmetry at the LHC instigated recent
interest in non-supersymmetric heterotic-string vacua. We explore what may be
learned in this context from the quasi--realistic free fermionic models. We
show that constructions with a low number of families give rise to
proliferation of a priori tachyon producing sectors, compared to the
non--realistic examples, which typically may contain only one such sector. The
reason being that in the realistic cases the internal six dimensional space is
fragmented into smaller units. We present one example of a quasi--realistic,
non--supersymmetric, non--tachyonic, heterotic--string vacuum and compare the
structure of its massless spectrum to the corresponding supersymmetric vacuum.
While in some sectors supersymmetry is broken explicitly, i.e. the bosonic and
fermionic sectors produce massless and massive states, other sectors, and in
particular those leading to the chiral families, continue to exhibit fermi-bose
degeneracy. In these sectors the massless spectrum, as compared to the
supersymmetric cases, will only differ in some local or global U(1) charges. We
discuss the conditions for obtaining at the massless level in these
models. Our example model contains an anomalous U(1) symmetry, which generates
a tadpole diagram at one loop-order in string perturbation theory. We speculate
that this tadpole diagram may cancel the corresponding diagram generated by the
one-loop non-vanishing vacuum energy and that in this respect the
supersymmetric and non-supersymmetric vacua should be regarded on equal
footing. Finally we discuss vacua that contain two supersymmetry generating
sectors.Comment: 31 pages. 10 tables. Minor corrections. Tables are amended. Published
versio
Monolayer honeycomb structures of group IV elements and III-V binary compounds
Using first-principles plane wave calculations, we investigate two
dimensional honeycomb structure of Group IV elements and their binary
compounds, as well as the compounds of Group III-V elements. Based on structure
optimization and phonon mode calculations, we determine that 22 different
honeycomb materials are stable and correspond to local minima on the
Born-Oppenheimer surface. We also find that all the binary compounds containing
one of the first row elements, B, C or N have planar stable structures. On the
other hand, in the honeycomb structures of Si, Ge and other binary compounds
the alternating atoms of hexagons are buckled, since the stability is
maintained by puckering. For those honeycomb materials which were found stable,
we calculated optimized structures, cohesive energies, phonon modes, electronic
band structures, effective cation and anion charges, and some elastic
constants. The band gaps calculated within Density Functional Theory using
Local Density Approximation are corrected by GW0 method. Si and Ge in honeycomb
structure are semimetal and have linear band crossing at the Fermi level which
attributes massless Fermion character to charge carriers as in graphene.
However, all binary compounds are found to be semiconductor with band gaps
depending on the constituent atoms. We present a method to reveal elastic
constants of 2D honeycomb structures from the strain energy and calculate the
Poisson's ratio as well as in-plane stiffness values. Preliminary results show
that the nearly lattice matched heterostructures of ...Comment: 12 Pages, 7 Figures, 1 Table;
http://link.aps.org/doi/10.1103/PhysRevB.80.15545
Case Report: Labial Veneer All Porcelain with Press Method for Improving Aesthetic on Patient with Central Diastema Case
Patients with central diastema disorders often feel shame and less of confident. The disorder can be repaired by a Labial veneer restoration. This restoration is an improvement in the form of a layer on the labial surface of the tooth selected because it gives satisfactory aesthetic results and maintains the tooth structure. At this time, the method of fabricating labial veneer all porcelain growing rapidly, such as making labial veneer all porcelain with base layer using press method like all porcelain E-max press. This paper aims to determine the stages and problem solving of the difficulties that arise in the procedure of fabricating labial veneer all porcelain with the basic layer of labial veneer using press method. The method is based on working model done in dental laboratory, starting from work model preparation, wax contouring (wax up), Sprueing, Investing, Preheating, Pressing, Divesting, Cutting sprue and Build-up porcelain. Results obtained from making this labial veneer all porcelain is a tightly closed diastema that forms a contact of the field, smooth and glossy surface and good aesthetic
Studi Tentang Pengaruh Hari Perdaganganterhadap Return Saham Pada Bursa Efek Indonesia
Penelitian ini bertujuan untuk menguji pengaruh hari perdagangan terhadap return sahamserta fenomena-fenomena yang berkaitan denganday of the week effect, yakni Monday effect, weekfour effect dan Rogalski effect. Populasi dalam penelitian ini adalah Perusahaan yang terdaftar dalam Indeks Saham LQ-45 di Bursa Efek Indonesia selama periode Januari – Desember 2014.Teknik pengambilan sampel menggunakan metode purposive sampling.Data yang digunakan dalam penelitian ini adalah data sekunder, diperoleh dari informasi yang tersedia di Bursa Efek Indonesia. Pengumpulan data dilakukan dengan studi dokumentasi.Metode yang digunakan adalah metode analisis deskriptif dan metode analisis statistik. Hasil pengujian dalam penelitian ini menunjukkan bahwa hari perdagangan tidak berpengaruh signifikan terhadap return saham harian pada Bursa Efek Indonesia tahun 2014. Hal ini tidak membuktikan bahwa terjadi fenomena day of week effect di Bursa Efek Indonesia, dimana return terendah terjadi pada hari Senin dan return tertinggi terjadi pada hari Selasa. Hasil empiris ini juga tidak membuktinya terjadinya Monday Effect pada Bursa Efek Indonesia pada tahun 2014. Fenomena week four effect juga tidak berhasil ditemukan pada Bursa Efek Indonesia pada tahun 2014, dimana return negatif signifikan terjadi pada hari Senin minggu keempat dan kelima setiap akhir bulan. Penelitian ini juga tidak berhasil menemukan bukti terjadinya adanya Rogalski Effect pada bulan April diBursa Efek Indonesia pada tahun 2014
Ballisticity of nanotube FETs: Role of phonon energy and gate bias
We investigate the role of electron-phonon scattering and gate bias in
degrading the drive current of nanotube MOSFETs. Our central results are: (i)
Optical phonon scattering significantly decreases the drive current only when
gate voltage is higher than a well-defined threshold. It means that elastic
scattering mechanisms are most detrimental to nanotube MOSFETs. (ii) For
comparable mean free paths, a lower phonon energy leads to a larger degradation
of drive current. Thus for semiconducting nanowire FETs, the drive current will
be more sensitive than carbon nanotube FETs because of the smaller phonon
energies in semiconductors. (iii) Radial breathing mode phonons cause an
appreciable reduction in drive current.Comment: 16 pages, 1 table, 4 figure
Peningkatan Keterampilan Generik Sains Dan Penguasaan Konsep Melalui Laboratorium Virtual Bebasis Inkuiri
Penelitian ini bertujuan untuk mengetahui peningkatan keterampilan generik sains dan penguasaan konsep pada materi arus listrik searah serta memperoleh gambaran respon mahasiswa terhadap penggunaan laboratorium virtual berbasis inkuiri. Penelitian ini dilakukan dengan metode pre-eksperimental design melalui one group pretest-posttest design yang dilaksanakan di Prodi Pendidikan Fisika Fakultas Tarbiyah dan Keguruan UIN Ar-Raniry Banda Aceh. Sampel yang terpilih menggunakan teknik porposive sampling yaitu angkatan 2014 unit 2 yang dijadikan kelas eksperimen. Pengumpulan data dilakukan dengan pretest dan posttest untuk mengetahui peningkatan keterampilan generik sains dan penguasaan konsep, lembar observasi untuk mengamati aktivitas mahasiswa selama proses pembelajaran, serta angket untuk mengetahui tanggapan mahasiswa terhadap penggunaan laboratorium virtual berbasis inkuiri. Hasil uji normalitas menunjukkan bahwa data N-gain berdistribusi normal. Persentase N-gain keterampilan generik sains tertinggi terjadi pada indikator kesadaran tentang skala sebesar 60% dengan kategori sedang dan terendah terjadi pada indikator pemodelan sebesar 27,81% dengan kategori rendah. Persentase rata-rata penguasaan konsep N-gain tertinggi pada sub konsep kuat arus dan beda potensial listrik sebesar 62,72% dan yang terendah pada sub konsep rangkaian hambatan listrik sebesar 33,33%. Mahasiswa memberikan tanggapan positif terhadap penggunaan laboratorium virtual berbasis inkuiri. Dapat disimpulkan penggunaan laboratorium virtual berbasis inkuiri dapat meningkatkan keterampilan generik sains dan penguasaan konsep
PENGEMBANGAN MODEL PERMAINAN GERAK DASAR LEMPAR UNTUK SISWA KELAS V SDN TAWANGARGO 4 KARANGPLOSO MALANG
Penelitian ini bertujuan mengembangkan permainan gerak dasar lempar bagi siswa kelas V di SDN Tawangargo 4 Karangploso Kabupaten Malang Jawa Timur. Metode penelitian yang digunakan adalah penelitian dan pengembangan dengan model konseptual. Prosedur penelitian meliputi: analisis kebutuhan, pengembangan produk, dan uji coba produk. Teknik analisis data yang digunakan adalah analisis data kualitatif dan kuantitatif. Hasil penelitian menunjukkan bahwa produk ini valid digunakan siswa kelas V di SDN Tawangargo 4 Karangploso Kabupaten Malang. Hasil uji coba kelompok kecil dan kelompok besar mendapat rata-rata persentase 89,26%. Angka tersebut menunjukkan bahwa model permainan ini praktis digunakan oleh siswa kelas V di SD dan efektif meningkatkan gerak dasar lempar kelas V SD. Kata Kunci: model permainan, gerak dasar lempar, siswa SD
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