Self-Organized Bottleneck in Energy Relaxation

We study an energy relaxation process after many degrees of freedom are excited in a Hamiltonian system with a large number of degrees of freedom. Bottlenecks of relaxation, where relaxations of the excited elements are drastically slowed down, are discovered. By defining an internal state for the excited degrees of freedom, it is shown that the drastic slowing down occurs when the internal state is in a critical state. The relaxation dynamics brings the internal state into the critical state, and the critical bottleneck of relaxation is self-organized. Relevance of our result to relaxation phenomena in condensed matters or large molecules is briefly discussed.Comment: 4pages, 5 figure

A Near-Infrared Spectroscopic Study of the Accreting Magnetic White Dwarf SDSS J121209.31+013627.7 and its Substellar Companion

The nature of the excess near-infrared emission associated with the magnetic white dwarf commonly known as SDSS 1212 is investigated primarily through spectroscopy, and also via photometry. The inferred low mass secondary in this system has been previously detected by the emission and variation of H$\alpha$, and the $1-2.5$ $\mu$m spectral data presented here are consistent with the presence of a late L or early T dwarf. The excess flux seen beyond 1.5 $\mu$m in the phase-averaged spectrum is adequately modeled with an L8 dwarf substellar companion and cyclotron emission in a 7 MG magnetic field. This interesting system manifests several observational properties typical of polars, and is most likely an old interacting binary with a magnetic white dwarf and a substellar donor in an extended low state.Comment: 28 pages, 5 figures, Accepted to Ap

Cool Customers in the Stellar Graveyard I: Limits to Extrasolar Planets Around the White Dwarf G29-38

We present high contrast images of the hydrogen white dwarf G 29-38 taken in the near infrared with the Hubble Space Telescope and the Gemini North Telescope as part of a high contrast imaging search for substellar objects in orbit around nearby white dwarfs. We review the current limits on planetary companions for G29-38, the only nearby white dwarf with an infrared excess due to a dust disk. We add our recent observations to these limits to produce extremely tight constraints on the types of possible companions that could be present. No objects $>$ 6 M$_{Jup}$ are detected in our data at projected separations $>$ 12 AU, and no objects $>$ 16 M$_{Jup}$ are detected for separations from 3 to 12 AU, assuming a total system age of 1 Gyr. Limits for companions at separations $<$ 3 AU come from a combination of 2MASS photometry and previous studies of G29-38's pulsations. Our imaging with Gemini cannot confirm a tentative claim for the presence of a low mass brown dwarf. These observations demonstrate that a careful combination of several techniques can probe nearby white dwarfs for large planets and low mass brown dwarfs.Comment: 20 pages, 4 figures, Accepted to Ap

Cool Customers in the Stellar Graveyard IV: Spitzer Search for Mid-IR excesses Around Five DAs

Hydrogen atmosphere white dwarfs with metal lines, so-called DAZs, require external accretion of material to explain the presence of weak metal line absorption in their photospheres. The source of this material is currently unknown, but could come from the interstellar medium, unseen companions, or relic planetesimals from asteroid belt or Kuiper belt analogues. Accurate mid-infrared photometry of these white dwarfs provide additional information to solve the mystery of this accretion and to look for evidence of planetary systems that have survived post main sequence evolution. We present {\em Spitzer} IRAC photometry accurate to $\sim$3% for four DAZs and one DA with circumstellar absorption lines in the UV. We search for excesses due to unseen companions or circumstellar dust disks. We use {\em Hubble Space Telescope} NICMOS imaging of these white dwarfs to gauge the level of background contamination to our targets as well as rule out common proper motion companions to WD 1620-391. All of our targets show no excesses due to companions $>$20 M$_{J}$, ruling out all but very low mass companions to these white dwarfs at all separations. No excesses due to circumstellar disks are observed, and we place limits on what types of disks may still be present.Comment: 18 pages, 8 figures, Accepted to A

Direct Dark Matter Detection with Velocity Distribution in the Eddington approach

Exotic dark matter together with the vacuum energy (associated with the cosmological constant) seem to dominate the Universe. Thus its direct detection is central to particle physics and cosmology. Supersymmetry provides a natural dark matter candidate, the lightest supersymmetric particle (LSP). One essential ingredient in obtaining the direct detection rates is the density and the velocity distribution of the LSP in our vicinity. In the present paper we study simultaneously density profiles and velocity distributions in the context of the Eddington approach. In such an approach, unlike the commonly assumed Maxwell-Boltzmann (M-B) distribution, the upper bound of the velocity arises naturally from the potential.Comment: 21 LaTex pages, 27 figure

Electronic doping of graphene by deposited transition metal atoms

We perform a phenomenological analysis of the problem of the electronic doping of a graphene sheet by deposited transition metal atoms, which aggregate in clusters. The sample is placed in a capacitor device such that the electronic doping of graphene can be varied by the application of a gate voltage and such that transport measurements can be performed via the application of a (much smaller) voltage along the graphene sample, as reported in the work of Pi et al. [Phys. Rev. B 80, 075406 (2009)]. The analysis allows us to explain the thermodynamic properties of the device, such as the level of doping of graphene and the ionisation potential of the metal clusters in terms of the chemical interaction between graphene and the clusters. We are also able, by modelling the metallic clusters as perfect conducting spheres, to determine the scattering potential due to these clusters on the electronic carriers of graphene and hence the contribution of these clusters to the resistivity of the sample. The model presented is able to explain the measurements performed by Pi et al. on Pt-covered graphene samples at the lowest metallic coverages measured and we also present a theoretical argument based on the above model that explains why significant deviations from such a theory are observed at higher levels of coverage.Comment: 16 pages, 10 figure

Implicit Solutions of PDE's

Further investigations of implicit solutions to non-linear partial differential equations are pursued. Of particular interest are the equations which are Lorentz invariant. The question of which differential equations of second order for a single unknown $\phi$ are solved by the imposition of an inhomogeneous quadratic relationship among the independent variables, whose coefficients are functions of $\phi$ is discussed, and it is shown that if the discriminant of the quadratic vanishes, then an implicit solution of the so-called Universal Field Equation is obtained. The relation to the general solution is discussed.Comment: 11 pages LaTeX2

Pengaruh Pemberian Air Kelapa Terhadap Pertumbuhan Bibit Pepaya (Carica papaya L)

Pepaya adalah salah satu komoditas yang dapat disantap dalam buah segar dan dapat dibuat dalam bentuk olahan. Penelitian ini bertujuan untuk mengetahui pengaruh pemberian air kelapa terhadap pertumbuhan bibit pepaya. Akan tetapi dalam penyediaan bibit sangat dipengaruhi benihnya. Hal ini menyebabkan perlunya bahan yang dapat meningkatkan pertumbuhan dari bibit. Penelitian ini bertujuan untuk pengaruh pemberian air kelapa terhadap pertumbuhan bibit pepaya (Carica papaya L). Penelitian dilaksanakan di Kebun Lapangan Pertanian Universitas Kristen Wira Wacana Sumba pada bulan September-November 2022. Penelitian menggunakan Rancangan Acak Lengkap (RAL) yang terdiri dari 5 perlakuan dan 4 ulangan sehingga jumlah unit percobaab 20 percobaan yaitu kontrol (A0), 10% air kelapa (A1), 20% air kelapa (A2), 30% air kelapa (A3), 30% air kelapa (A3), 40% air kelapa (A4). Hasil penelitian menunjukkan pemberian air kelapa pada perlakuan 30% memberikan presentase rata-rata tertinggi pada pengamatan variabel jumlah daun, tinggi tanaman dan diameter batan

Slow relaxation to equipartition in spring-chain systems

In this study, one-dimensional systems of masses connected by springs, i.e., spring-chain systems, are investigated numerically. The average kinetic energy of chain-end particles of these systems is larger than that of other particles, which is similar to the behavior observed for systems made of masses connected by rigid links. The energetic motion of the end particles is, however, transient, and the system relaxes to thermal equilibrium after a while, where the average kinetic energy of each particle is the same, that is, equipartition of energy is achieved. This is in contrast to the case of systems made of masses connected by rigid links, where the energetic motion of the end particles is observed in equilibrium. The timescale of relaxation estimated by simulation increases rapidly with increasing spring constant. The timescale is also estimated using the Boltzmann-Jeans theory and is found to be in quite good agreement with that obtained by the simulation

Weyl asymptotics: From closed to open systems

We present microwave experiments on the symmetry reduced 5-disk billiard studying the transition from a closed to an open system. The measured microwave reflection signal is analyzed by means of the harmonic inversion and the counting function of the resulting resonances is studied. For the closed system this counting function shows the Weyl asymptotic with a leading exponent equal to 2. By opening the system successively this exponent decreases smoothly to an non-integer value. For the open systems the extraction of resonances by the harmonic inversion becomes more challenging and the arising difficulties are discussed. The results can be interpreted as a first experimental indication for the fractal Weyl conjecture for resonances.Comment: 9 pages, 7 figure