Quasinormal modes of Kerr-Newman black holes: coupling of electromagnetic and gravitational perturbations

We compute numerically the quasinormal modes of Kerr-Newman black holes in the scalar case, for which the perturbation equations are separable. Then we study different approximations to decouple electromagnetic and gravitational perturbations of the Kerr-Newman metric, computing the corresponding quasinormal modes. Our results suggest that the Teukolsky-like equation derived by Dudley and Finley gives a good approximation to the dynamics of a rotating charged black hole for Q<M/2. Though insufficient to deal with Kerr-Newman based models of elementary particles, the Dudley-Finley equation should be adequate for astrophysical applications.Comment: 13 pages, 3 figures. Minor changes to match version accepted in Phys. Rev.

Double Compact Objects III: Gravitational Wave Detection Rates

The unprecedented range of second-generation gravitational-wave (GW) observatories calls for refining the predictions of potential sources and detection rates. The coalescence of double compact objects (DCOs)---i.e., neutron star-neutron star (NS-NS), black hole-neutron star (BH-NS), and black hole-black hole (BH-BH) binary systems---is the most promising source of GWs for these detectors. We compute detection rates of coalescing DCOs in second-generation GW detectors using the latest models for their cosmological evolution, and implementing inspiral-merger-ringdown (IMR) gravitational waveform models in our signal-to-noise ratio calculations. We find that: (1) the inclusion of the merger/ringdown portion of the signal does not significantly affect rates for NS-NS and BH-NS systems, but it boosts rates by a factor $\sim 1.5$ for BH-BH systems; (2) in almost all of our models BH-BH systems yield by far the largest rates, followed by NS-NS and BH-NS systems, respectively, and (3) a majority of the detectable BH-BH systems were formed in the early Universe in low-metallicity environments. We make predictions for the distributions of detected binaries and discuss what the first GW detections will teach us about the astrophysics underlying binary formation and evolution.Comment: published in ApJ, 19 pages, 11 figure

Comment on `Hawking radiation from fluctuating black holes'

Takahashi & Soda (2010 Class. Quantum Grav. v27 p175008, arXiv:1005.0286) have recently considered the effect (at lowest non-trivial order) of dynamical, quantized gravitational fluctuations on the spectrum of scalar Hawking radiation from a collapsing Schwarzschild black hole. However, due to an unfortunate choice of gauge, the dominant (even divergent) contribution to the coefficient of the spectrum correction that they identify is a pure gauge artifact. I summarize the logic of their calculation, comment on the divergences encountered in its course and comment on how they could be eliminated, and thus the calculation be completed.Comment: 12 pages, 1 fig; feynmp, amsref

Persepsi Peserta Didik Terhadap Pembelajaran Ilmu Pengetahuan Alam Berbasis e-Learning Saat Situasi Pandemi Covid-19 Kelas VII

This study aims to determine the students perception of science learning based on e-learning in the pandemic situation. The research design used was descriptive. The research sample was take from participants with purposive sampling technique obtained by 162 students. The data from this research used the likert qestionnaire sheets, with entered into the google form. The results score data from the questionnaire will be calculated with used presentation statistic. The results showed that the form obtainde of positive anda negative questionnaires. The positive questionnaire obtained 373,1% very agree, 1112,8% agree, 274,4% disagree, and 40% very disagree. The negative questionnaire obtained 125,8%  very agree, 554% agree, 431,9% disagree, and 88,5% very disagree.Penelitian ini bertujuan untuk mengetahui persepsi peserta didik terhadap pembelajaran Ilmu Pengetahuan Alam berbasis e-learning saat situasi pandemi. Desain yang digunakan dalam penelitian ini adalah deskriptif. Sampel penelitian sebanyak 162 peserta didik yang dipilih melalui teknik Purposive Sampling. data pada penelitian ini adalah lembar angket likert yang dimasukkan ke dalam Google Form secara online sebagai bantu yang dipilih dan digunakan oleh peneliti dalam kegiatan mengumpulkan data penelitian. Hasil penelitian menunjukan bahwa didapatkan hasil angket positif dan negatif. Pada angket positif didapatkan sebanyak 373,1% menyatakan sangat setuju, 1112,8% menyatakan setuju, 274,4% menyatakan tidak setuju, dan 40% menyatakan sangat tidak setuju. Sedangkan pada hasil angket negatif didapatkan sebanyak 125,8% menyatakan sangat setuju, 554% menyatakan setuju, 431,9% menyatakan tidak setuju, dan 88,5% menyatakan sangat tidak setuju. Kata kunci: e-learning, Ilmu Pengetahuan Alam, perseps

Gravitational signals emitted by a point mass orbiting a neutron star: a perturbative approach

We compute the energy spectra of the gravitational signals emitted when a pointlike mass moves on a closed orbit around a non rotating neutron star, inducing a perturbation of its gravitational field and its internal structure. The Einstein equations and the hydrodynamical equations are perturbed and numerically integrated in the frequency domain. The results are compared with the energy spectra computed by the quadrupole formalism which assumes that both masses are pointlike, and accounts only for the radiation emitted because the orbital motion produces a time dependent quadrupole moment. The results of our perturbative approach show that, in general, the quadrupole formalism overestimates the amount of emitted radiation, especially when the two masses are close. However, if the pointlike mass is allowed to move on an orbit so tight that the keplerian orbital frequency resonates with the frequency of the fundamental quasi-normal mode of the star (2w_K=w_f), this mode can be excited and the emitted radiation can be considerably larger than that computed by the quadrupole approach.Comment: 36 pages, 7 figures, submimtted to Phys. Rev.

Integrasi TPACK Dalam Flipped Learning Untuk Meningkatkan Keterampilan Berpikir Kritis Peserta Didik Pada Pembelajaran Biologi di SMAN 1 Metro

TPACK menjadi syarat implementasi pembelajaran berbasis teknologi. Integrasi TPACK pada model pembelajaran flipped learning dapat memfasilitasi pelaksanaan pembejaran secara online ataupun blended learning. Penelitian ini bertujuan untuk menganalisis integrasi TPACK dalaml Flipped Learning  terhadap keterampilan berpikir kritis peserta didik kelas XI SMA Negeri 1 Metro. Penelitian ini menggunakan quasi experiment dengan desain pretest- posttest nonequivalent groups design. Sampel yang digunakan di dalam penelitian ini berjumlah 61 orang yang terbagi menjadi Kelas XI IPA 3 (30 orang) dan Kelas XI IPA 3 (31 orang) dengan teknik pengambilan sampel yaitu purposive sampling. Data dalam penelitian ini berupa data kuantitatif dan data kualitatif. Data kuantitatif berupa data hasil berpikir kritis dari pretest, posttest dan nilai n-gain  selanjutnya dianalisis dengan uji Independent Sample t-test (α=0,05). Hasil penelitian meunjukkan bahwa terdapat pengaruh yang signifikan dari penerapan model Flipped Learning  terhadap keterampilan berpikir kritis peserta didik (Sig. p0,05). Data kualitatif berupa data nilai angket keterlaksanaan pembelajaran dengan skor 88,95% (kategori sangat baik) untuk hasil penilaian observer dan skor 64, 8 (kategori baik) untuk penilaian dari peserta didik. Sebanyak 67,4% peserta didik merasa dapat berpikir secara lebih kritis pada penerapan Flipped Learning. Dengan demikian, integrasi TPACK dalam Flipped Learning berpengaruh terhadap keterampilan berpikir kritis peserta didik dalam pembelajaran biologi secara daring

Komik Digital Sistem Peredaran Darah dan Pengaruhnya Pada Literasi Sains Peserta Didik

This study aims to determine the effect of using digital comics on the scientific literacy of class VIII students on the human circulatory system at SMP Negeri 3 Natar. The research sample of 32 students in class VIIIA as the experimental class and 32 students in class IIC as the control class were selected using a purposive sampling technique. The research design used a quasi-experimental non-equivalent control group design. The type of data used is quantitative data in the form of scientific literacy test questions and qualitative data using students' responsibility questionnaires for digital comics. The results showed that the value of Sig. (2-tailed) 0.000 0.005 so that H1 is accepted and H0 is rejected, so the use of digital comics has a significant effect on students' scientific literacy. Student responses in this study were in the good category (80%).Penelitian ini bertujuan untuk mengetahui pengaruh pemanfaatan komik digital terhadap literasi sains peserta didik kelas VIII materi sistem peredaran darah manusia di SMP Negeri 3 Natar. Sampel penelitian sebanyak 32 peserta didik kelas VIIIA sebagai kelas eksperimen dan 32 peserta didik kelas VIIIC sebagai kelas kontrol dipilih menggunakan teknik purposive sampling. Desain penelitian ini menggunakan quasi eksperimental tipe non-equivalent control grup design. Jenis data yang digunakan yaitu data kuantitatif dalam bentuk soal tes literasi sains dan data kualitatif dengan angket responsibility peserta didik terhadap komik digital. Hasil penelitian menunjukkan bahwa nilai Sig. (2-tailed) 0,000 0,005 sehingga H1 diterima dan H0 ditolak, sehingga penggunaan komik digital berpengaruh signifikan terhadap literasi sains peserta didik. Respon siswa dalam pembelajaran ini berkategori baik (80%). Kata kunci: literasi sains, komik digital, peserta didi

Periodic solutions for a class of nonlinear partial differential equations in higher dimension

We prove the existence of periodic solutions in a class of nonlinear partial differential equations, including the nonlinear Schroedinger equation, the nonlinear wave equation, and the nonlinear beam equation, in higher dimension. Our result covers cases where the bifurcation equation is infinite-dimensional, such as the nonlinear Schroedinger equation with zero mass, for which solutions which at leading order are wave packets are shown to exist.Comment: 34 page

Time quasi-periodic gravity water waves in finite depth

We prove the existence and the linear stability of Cantor families of small amplitude time quasi-periodic standing water wave solutions\u2014namely periodic and even in the space variable x\u2014of a bi-dimensional ocean with finite depth under the action of pure gravity. Such a result holds for all the values of the depth parameter in a Borel set of asymptotically full measure. This is a small divisor problem. The main difficulties are the fully nonlinear nature of the gravity water waves equations\u2014the highest order x-derivative appears in the nonlinear term but not in the linearization at the origin\u2014and the fact that the linear frequencies grow just in a sublinear way at infinity. We overcome these problems by first reducing the linearized operators, obtained at each approximate quasi-periodic solution along a Nash\u2013Moser iterative scheme, to constant coefficients up to smoothing operators, using pseudo-differential changes of variables that are quasi-periodic in time. Then we apply a KAM reducibility scheme which requires very weak Melnikov non-resonance conditions which lose derivatives both in time and space. Despite the fact that the depth parameter moves the linear frequencies by just exponentially small quantities, we are able to verify such non-resonance conditions for most values of the depth, extending degenerate KAM theory