Do Newton's G and Milgrom's a_0 vary with cosmological epoch ?

In the scalar tensor gravitational theories Newton's constant G_N evolves in the expanding universe. Likewise, it has been speculated that the acceleration scale a_0 in Milgrom's modified Newtonian dynamics (MOND) is tied to the scale of the cosmos, and must thus evolve. With the advent of relativistic implementations of the modified dynamics, one can address the issue of variability of the two gravitational ''constants'' with some confidence. Using TeVeS, the Tensor-Vector-Scalar gravitational theory, as an implementation of MOND, we calculate the dependence of G_N and a_0 on the TeVeS parameters and the coeval cosmological value of its scalar field, \phi_c. We find that G_N, when expressed in atomic units, is strictly nonevolving, a result fully consistent with recent empirical limits on the variation of G_N. By contrast, we find that a_0 depends on \phi_c and may thus vary with cosmological epoch. However, for the brand of TeVeS which seems most promising, a_0 variation occurs on a timescale much longer than Hubble's, and should be imperceptible back to redshift unity or even beyond it. This is consistent with emergent data on the rotation curves of disk galaxies at significants redshifts.Comment: 9 pages, RevTe

Kalsifikasi Skeleton Aksial Pada Regenerat Ekor Kadal {Mabouya multifasciata Kuhl)

Kadal {Mabouya multifasciata Kuhl) merupakan salah satu anggota Lacertilia yang terdapat di Indonesia yang dapat mengalami regenerasi setelah hewan tersebut mengalami autotomi ekor. Penelitian ini bertujuan untuk mengetahui kalsifikasi yang terjadi pada skeleton aksial regenerat ekor kadal. Empat puluhdelapan ekor kadal jantan dewasa berekor asli diautotomi ekornya, dipelihara, dan dibagi menjadi 4 kelompok yang terdiri dari 12 individu ( kelompok I, kelompok II, kelompok III, kelompok IV), masing-masing kelompck berturut-turut mempunyai umur regenerat 4,5,6, dan 12 minggu. Setelah itu dibuat preparat utuh regenerat ekor dengan pewamaan Alizarin RedS-Alcian Blue dan preparat irisan melintang regenerat ekor dengan pewamaan perak nitrat von Kossa. Hasil penelitian menunjukkan bahwa penulangan secara endokondralis diawali dengan kalsifikasi pada scbagian sisi dalam dan sebagian sisi luar tabung tulang rawan regenerat ekor umur 5 minggu. Pada regenerat ekor berumur 6 dan 12 minggu kalsifikasi sudah meluas ke_seluruh sisi dalam dan sisi luar tabung tulang rawan. Kata kunci: kalsifikasi, skeleton aksial, regenerat ekor, kada

A quest for frustration driven distortion in Y2Mo2O7

We investigated the nature of the freezing in the geometrically frustrated Heisenberg spin-glass Y2Mo2O7 by measuring the temperature dependence of the static internal magnetic field distribution above the spin-glass temperature, Tg, using the muSR technique. The evolution of the field distribution cannot be explained by changes in the spin susceptibility alone and suggests a lattice deformation. This possibility is addressed by numerical simulations of the Heisenberg Hamiltonian with magneto-elastic coupling at T>0.Comment: 5 pages 4 figures. Accepted for publication in PR

Abnormal Long-range Spatial Interactions in Amblyopia

AbstractNeural interactions between widely separated stimuli were explored with psychophysical and visual evoked potential (VEP) measures in normal and amblyopic observers. Contrast detection thresholds were measured psychophysically for small foveally viewed Gabor patches presented in isolation and in the presence of similar, but laterally displaced flanks. The amplitude and phase of VEPs elicited by similar targets were also measured. The presence of neural interaction between the target and flank responses was assessed by comparing the unflanked threshold to the flanked threshold in the psychophysical experiments and by comparing the response predicted by the algebraic sum of test and flank responses to that measured when test and flanks were presented simultaneously. In normal observers simultaneous presentation of test and flank targets produces a VEP response that is up to a factor of two larger than the linear prediction (facilitation). Psychophysical threshold is also facilitated by a comparable factor. Facilitation was found mainly for configurations in which local (carrier) and global (patch) orientations resulted in collinearity, independent of global orientation (meridian). Amblyopic observers showed several deviations from the normal pattern. The facilitation for the collinear configurations was either markedly lower than normal or was replaced by inhibition. The normal pattern of spatial interaction may facilitate the grouping of collinear line segments into smooth curves. In contrast, abnormal long-range spatial interactions may underlie the grouping disorders and perceptual distortions found in amblyopia. © 1997 Elsevier Science Ltd. All rights reserved

2,3,7,8-TETRAKLORODIBENZO-P-DIOKSIN (TCDD) MEMACU AKTIVITAS BIOSINTESIS PROTEIN DI JARINGAN PALATUM EMBRIO MENCIT

Bahan pencemar dioksin 2,3,7,8-Tetraklorodibenzo-p-dioksin (TCDD) yang diberikan pada mencit bunting menyebabkan janin yang dihasilkan menderita cacat cleft palate, dengan ciri bilah palatum kerdil atau bilah palatum tumbuh pendek. Telah dilakukan penelitian untuk menguji apakah pengurangan biosintesis protein terlibat sebagai mekanisme yang mendasari hambatan pertumbuhan bilah palatum oleh TCDD. Delapan ekor mencit bunting dibagi ke dalam empat kelompok, masing-masing diberi TCDD dosis 0, 5, 10, atau 20 μg/kg berat badan pada hari ke-12 kebuntingan. Besaran aktivitas biosintesis protein jaringan palatum embrio ditentukan dengan teknik AgNOR pada sediaan histologis irisan jaringan kraniofasial embrio usia kebuntingan hari ke-15. Nucleolar Organizing Region (NOR) adalah tempat biogenesis ribosom di inti sel yang jumlahnya meningkat seiring dengan peningkatan aktivitas biosintesis protein sel. Rataan jumlah butir AgNOR sel-sel jaringan palatum yang terendah adalah 2,51±0,167 untuk perlakuan 0 μg/kg bb (kontrol), dan berturut-turut 2,87±0,146, 2,87±0,190, dan 2,88±0,160 untuk perlakuan dosis 5, 10, dan 20 μg/kg bb. Jumlah butir AgNOR pada seluruh kelompok yang diberi TCDD lebih tinggi dibandingkan dengan jumlah butir AgNOR pada kontrol (P < 0,05). Disimpulkan, pengurangan biosintesis protein bukanlah mekanisme yang mendasari hambatan pertumbuhan palatum mencit oleh TCDD. Diduga, peningkatan biosintesis protein oleh TCDD menimbulkan kekacauan keseimbangan protein-protein faktor tumbuh di jaringan palatum dan mengakibatkan gangguan pertumbuhan dan diferensias

Choices: The Science of Bela Julesz

Highlights of Bela Julesz's scientific career in visual neuroscienc

Ramsey-like measurement of the decoherence rate between Zeeman sub-levels

Two-photon processes that involve different sub-levels of the ground state of an atom, are highly sensitive to depopulation and decoherence within the ground state. For example, the spectral width of electromagnetically induced transparency resonances in $\Lambda-$type system, are strongly affected by the ground state depopulation and decoherence rates. We present a direct measurement of decay rates between hyperfine and Zeeman sub-levels in the ground state of $^{87}$Rb vapor. Similar to the relaxation-in-the-dark technique, pumping lasers are used to pre-align the atomic vapor in a well defined quantum state. The free propagation of the atomic state is monitored using a Ramsey-like method. Coherence times in the range 1-10 ms were measured for room temperature atomic vapor. In the range of the experimental parameters used in this study, the dominant process inducing Zeeman decoherence is the spin-exchange collisions between rubidium atoms.Comment: 7 pages, 7 figure

Preferred frame parameters in the tensor-vector-scalar theory of gravity and its generalization

The Tensor-Vector-Scalar theory of gravity, which was designed as a relativistic implementation to the modified dynamics paradigm, has fared quite well as an alternative to dark matter, on both galactic and cosmological scales. However, its performance in the solar system, as embodied in the post-Newtonian formalism, has not yet been fully investigated. Tamaki has recently attempted to calculate the preferred frame parameters for TeVeS, but ignored the cosmological value of the scalar field, thus concluding that the Newtonian potential must be static in order to be consistent with the vector equation. We show that when the cosmological value of the scalar field is taken into account, there is no constraint on the Newtonian potential; however, the cosmological value of the scalar field is tightly linked to the vector field coupling constant K, preventing the former from evolving as predicted by its equation of motion. We then proceed to investigate the post-Newtonian limit of a generalized version of TeVeS, with {\AE}ther type vector action, and show that its \beta,\gamma and \xi parameters are as in GR, while solar system constraints on the preferred frame parameters \alpha_1 and \alpha_2 can be satisfied within a modest range of small values of the scalar and vector fields coupling parameters, and for values of the cosmological scalar field consistent with evolution within the framework of existing models.Comment: 16 pages, 2 figures Figures and corresponding discussion replaced; added reference

Antigen and Thapsigargin Promote Influx of Ca2+ in Rat Basophilic RBL-2H3 Cells by Ostensibly Similar Mechanisms That Allow Filling of Inositol 1,4,5-Trisphosphate-Sensitive and Mitochondrial Ca2+ Stores

In single, Fura 2-loaded RBL-2H3 cells, antigen and thapsigargin depleted the same intracellular pool of Ca2+ in the absence of external Ca2+; provision of external Ca2+ induced immediate increases in levels of free Ca2+ ([Ca2+](i)). These increases were dependent on the presence of external Ca2+ and, presumably, on influx of Ca2+ across the cell membrane. Both stimulants enhanced intracellular accumulation of 45Ca2+ through ostensibly similar mechanisms because accumulation was blocked to similar extents by various multivalent cations or by depolarization with K+. Because thapsigargin blocked reuptake of Ca2+ into inositol 1,4,5-trisphosphate sensitive stores, uptake occurred independently of the refilling of these stores. Uptake was dependent instead on sequestration of 45Ca2+ in a pool of high capacity that was insensitive to thapsigargin, caffeine, GTP and inositol 1,4,5-trisphosphate but sensitive to ionomycin and mitochondrial inhibitors. The existence of an inositol 1,4,5-trisphosphate-insensitive pool was also apparent in permeabilized cells; at 0.1 μM [Ca2+](i), uptake of 45Ca2+ was largely confined (\u3e 80%) to the inositol 1,4,5-trisphosphate-sensitive pool, but at 2 μM [Ca2+](i) uptake was largely (\u3e 60%) into the inositol 1,4,5-trisphosphate-insensitive pool. Provision of mitochondrial inhibitors along with thapsigargin to block uptake into both pools, did not impair the thapsigargin-induced increase in [Ca2+](i) or influx of Ca2+, as indicated by changes in Fura 2 fluorescence, but did block the intracellular accumulation of 45Ca2+. The studies illustrate the utility of simultaneous measurements of [Ca2+](i) and 45Ca2+ uptake for a full accounting of Ca2+ homoeostasis as exemplified by the ability to distinguish between influx and mitochondrial uptake of Ca2+