We present results from the first directed search for nontensorial gravitational waves. While general relativity allows for tensorial (plus and cross) modes only, a generic metric theory may, in principle, predict waves with up to six different polarizations. This analysis is sensitive to continuous signals of scalar, vector, or tensor polarizations, and does not rely on any specific theory of gravity. After searching data from the first observation run of the advanced LIGO detectors for signals at twice the rotational frequency of 200 known pulsars, we find no evidence of gravitational waves of any polarization. We report the first upper limits for scalar and vector strains, finding values comparable in magnitude to previously published limits for tensor strain. Our results may be translated into constraints on specific alternative theories of gravity.

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Global stability modes of flows provide significant insight into their dynamics. Direct methods to obtain these modes are restricted by the daunting sizes and complexity of Jacobians encountered in general three-dimensional flows. Jacobian-free approaches have greatly alleviated the required computational burden. Particularly, the most common Arnoldi-based methods obtain the desired subset of the eigenmodes by considering Jacobian-vector products to create a smaller iterative subspace, instead of working with the Jacobian itself. However, operations such as orthonormalization and shift-and-invert transformation of matrices with appropriate shift guesses can introduce computational and parameter-dependent costs that inhibit their routine application to general three-dimensional flowfields. Further, in time-stepper type approaches, where the linearized perturbation snapshots directly obtained from an aerodynamic code are treated as Jacobian-vector products, the inversion operation necessitates use of approximate iterative linear solvers with several parameters. The present work addresses these limitations by proposing and implementing a robust, generalizable approach to extract the principal global modes, suited for curvilinear coordinates as well as the effects of compressibility. Accurate linearized perturbation snapshots are obtained using high-order schemes by leveraging the same non-linear Navier-Stokes code as used to obtain the basic state by appropriately constraining the equations using a body-force. The forcing includes not only that required to obtain the products, but also to ensure that the basic state does not drift.It is shown that with random impulse forcing, dynamic mode decomposition (DMD) of the subspace formed by these products yields the desired physically meaningful modes, when appropriately scaled. The leading eigenmodes are thus obtained without spurious modes or the need for an iterative procedure. Further since orthonormalization is not required, large subspaces can be processed to capture converged low frequency or stationary modes. The validity and versatility of the method is demonstrated with numerous examples encompassing essential elements expected in realistic flows, such as compressibility effects and complicated domains requiring general curvilinear meshes. Favorable qualitative as well as quantitative comparisons with Arnoldi-based method, complemented with substantial savings in computational resources show the potential of current approach for relatively complex flows.

An experimental search for new forces coupling to nuclear isospin with a range of >3 m was conducted using a torsion balance driven in resonance by a set of masses configured to generate a nearly pure isospin source field. The strength of any such coupling § in units of gravity per atomic mass unit is found to be bounded by -2.3x 10~4< §< 4-2.7x 10 ~5, where the positive sign represents an attractive force between like isospin charges.PACS numbers: 04.90.+e, 14.80.Pb Experimental searches 1 for new intermediate-range forces weaker than gravity during the last three years have yielded much valuable information, even though, as yet, they have failed to provide any generally accepted positive evidence for the existence of such a force at the level first suggested by the reanalysis of the Eotvos experiment and by the mine-gravity data. 2 The hypothetical force is usually represented by a Yukawa potential which, when added to the standard Newtonian gravitational potential, reads as K(r)--Gmim 2 r" 1 [14-aexp(-rA)] , where a is the new coupling in units of gravity and X is its range. The composition dependence can be made explicit by writing a ^qiq^ with qi-cosO(N + Z)i/tii + sin9(N-Z)i/iii , where the new effective charge has been written as a linear combination of the baryon number and nuclear isospin per atomic mass unit, in standard notation. In the present paper we assume a pure isospin coupling, i.e., 0 = K/2 and q t -(TV -Z)//^,. We have modified our } earlier configuration of source masses so as to increase the expected signal for an isospin coupling and to suppress, further, the effects of gravity and its gradients on the pendulum. This has enabled us to extend the search for isopin-dependent forces to considerably higher levels of sensitivity than those reported earlier, the present measurement being characterized by the ability to measure differential accelerations of -5xlO" 13 cms~2.A brief description of the apparatus can be found in Refs. l(j) and 3. The torsion pendulum consists of two semicircular rings of copper and lead each of mean radius about 8.5 cm and mass about 700 g joined along their diameters; two pairs of grooves in the lead make its mass distribution match closely that of the copper half, l(j)3 to reduce the coupling of the ring to gradients in the gravity field. This dual ring is suspended with its plane horizontal ix-y plane) by means of a tungsten fiber 250 cm long and 105 /xm in diameter inside a vacuum chamber with pressure below 10 ~8 Torr. But for imperfections of fabrication and small tilts of the ring, the quadrupole moment tensor Q of the ring is diagonal and also has the property Q xx ^Qyy. An optical-quality mirror, in an assembly weighing about 35 g, is attached to the ring at a height of 40 cm and within about 0.1 cm of the fiber axis. An autocollimating optical lever views this mirror and yields the angular orientation of the ring with an accuracy of 5xl0~9 rad/Hz 1/2 . The natural period of torsional oscillation of the pendulum was measured to be 795.6 s; this corresponds to...

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