4,189 research outputs found
High floc strength with aged polyelectrolytes
The ageing of powdered polyelectrolyte solutions has shown that while the viscosity of these solutions decreases rapidly with time, the flocculation performance and the strength of the flocs produced does not alter over periods >200 days. This was shown for polyacrylamides of cationic, anionic and non-ionic charge. The use of tap or deionized water did not adversely affect the results unless a biocide capable of associating with the polyelectrolyte was added. These results contradict the common belief that solutions made with powdered polyelectrolytes should not be stored for long periods of time as their performance decreases after being stored for several days. The results indicate that powdered polyelectrolyte solutions are suitable for intermittent process operations, such as sewer overflow treatment and that dosing and handling of the solutions can be made easier by ageing of the solutions
Heterotic domain wall solutions and SU(3) structure manifolds
We examine compactifications of heterotic string theory on manifolds with
SU(3) structure. In particular, we study N = 1/2 domain wall solutions which
correspond to the perturbative vacua of the 4D, N =1 supersymmetric theories
associated to these compactifications. We extend work which has appeared
previously in the literature in two important regards. Firstly, we include two
additional fluxes which have been, heretofore, omitted in the general analysis
of this situation. This allows for solutions with more general torsion classes
than have previously been found. Secondly, we provide explicit solutions for
the fluxes as a function of the torsion classes. These solutions are
particularly useful in deciding whether equations such as the Bianchi
identities can be solved, in addition to the Killing spinor equations
themselves. Our work can be used to straightforwardly decide whether any given
SU(3) structure on a six-dimensional manifold is associated with a solution to
heterotic string theory. To illustrate how to use these results, we discuss a
number of examples taken from the literature.Comment: 34 pages, minor corrections in second versio
Nongeometry, Duality Twists, and the Worldsheet
In this paper, we use orbifold methods to construct nongeometric backgrounds,
and argue that they correspond to the spacetimes discussed in \cite{dh,wwf}.
More precisely, we make explicit through several examples the connection
between interpolating orbifolds and spacetime duality twists. We argue that
generic nongeometric backgrounds arising from duality twists will not have
simple orbifold constructions and then proceed to construct several examples
which do have a consistent worldsheet description.Comment: v2-references added; v3-minor correction (eqn. 4.17
Stabilizing the Complex Structure in Heterotic Calabi-Yau Vacua
In this paper, we show that the presence of gauge fields in heterotic
Calabi-Yau compacitifications causes the stabilisation of some, or all, of the
complex structure moduli of the Calabi-Yau manifold while maintaining a
Minkowski vacuum. Certain deformations of the Calabi-Yau complex structure,
with all other moduli held fixed, can lead to the gauge bundle becoming
non-holomorphic and, hence, non-supersymmetric. This leads to an F-term
potential which stabilizes the corresponding complex structure moduli. We use
10- and 4-dimensional field theory arguments as well as a derivation based
purely on algebraic geometry to show that this picture is indeed correct. An
explicit example is presented in which a large subset of complex structure
moduli is fixed. We demonstrate that this type of theory can serve as the
hidden sector in heterotic vacua and can co-exist with realistic particle
physics.Comment: 17 pages, Late
The Geometry of D=11 Killing Spinors
We propose a way to classify all supersymmetric configurations of D=11
supergravity using the G-structures defined by the Killing spinors. We show
that the most general bosonic geometries admitting a Killing spinor have at
least a local SU(5) or an (Spin(7)\ltimes R^8)x R structure, depending on
whether the Killing vector constructed from the Killing spinor is timelike or
null, respectively. In the former case we determine what kind of local SU(5)
structure is present and show that almost all of the form of the geometry is
determined by the structure. We also deduce what further conditions must be
imposed in order that the equations of motion are satisfied. We illustrate the
formalism with some known solutions and also present some new solutions
including a rotating generalisation of the resolved membrane solutions and
generalisations of the recently constructed D=11 Godel solution.Comment: 36 pages. Typos corrected and discussion on G-structures improved.
Final version to appear in JHE
Subaru weak-lensing study of A2163: bimodal mass structure
We present a weak-lensing analysis of the merging cluster A2163 using
Subaru/Suprime-Cam and CFHT/Mega-Cam data and discuss the dynamics of this
cluster merger, based on complementary weak-lensing, X-ray, and optical
spectroscopic datasets. From two dimensional multi-component weak-lensing
analysis, we reveal that the cluster mass distribution is well described by
three main components, including a two component main cluster A2163-A with mass
ratio 1:8, and its cluster satellite A2163-B. The bimodal mass distribution in
A2163-A is similar to the galaxy density distribution, but appears as spatially
segregated from the brightest X-ray emitting gas region. We discuss the
possible origins of this gas-dark matter offset and suggest the gas core of the
A2163-A subcluster has been stripped away by ram pressure from its dark matter
component. The survival of this gas core to the tidal forces exerted by the
main cluster let us infer a subcluster accretion with a non-zero impact
parameter. Dominated by the most massive component of A2163-A, the mass
distribution of A2163 is well described by a universal Navarro-Frenk-White
profile as shown by a one-dimensional tangential shear analysis, while the
singular-isothermal sphere profile is strongly ruled out. Comparing this
cluster mass profile with profiles derived assuming intracluster medium
hydrostatic equilibrium (H.E.) in two opposite regions of the cluster
atmosphere has allowed us to confirm the prediction of a departure from H.E. in
the eastern cluster side, presumably due to shock heating. Yielding a cluster
mass estimate of M_{500}=11.18_{-1.46}^{+1.64}\times10^{14}h^{-1}Msun, our mass
profile confirm the exceptionally high mass of A2163, consistent with previous
analyses relying on the cluster dynamical analysis and Yx mass proxy.Comment: 17 pages, 11 figures, ApJ, in press. Full resolution version is
available at http://www.asiaa.sinica.edu.tw/~okabe/files/a2163_WL_astroph.pd
Nongeometric Flux Compactifications
We investigate a simple class of type II string compactifications which
incorporate nongeometric "fluxes" in addition to "geometric flux" and the usual
H-field and R-R fluxes. These compactifications are nongeometric analogues of
the twisted torus. We develop T-duality rules for NS-NS geometric and
nongeometric fluxes, which we use to construct a superpotential for the
dimensionally reduced four-dimensional theory. The resulting structure is
invariant under T-duality, so that the distribution of vacua in the IIA and IIB
theories is identical when nongeometric fluxes are included. This gives a
concrete framework in which to investigate the possibility that generic string
compactifications may be nongeometric in any duality frame. The framework
developed in this paper also provides some concrete hints for how mirror
symmetry can be generalized to compactifications with arbitrary H-flux, whose
mirrors are generically nongeometric.Comment: 26 pages, JHEP3. v3: references, minor corrections, and
clarifications added. v4: sign correcte
An accurate determination of the Avogadro constant by counting the atoms in a 28Si crystal
The Avogadro constant links the atomic and the macroscopic properties of
matter. Since the molar Planck constant is well known via the measurement of
the Rydberg constant, it is also closely related to the Planck constant. In
addition, its accurate determination is of paramount importance for a
definition of the kilogram in terms of a fundamental constant. We describe a
new approach for its determination by "counting" the atoms in 1 kg
single-crystal spheres, which are highly enriched with the 28Si isotope. It
enabled isotope dilution mass spectroscopy to determine the molar mass of the
silicon crystal with unprecedented accuracy. The value obtained, 6.02214084(18)
x 10^23 mol^-1, is the most accurate input datum for a new definition of the
kilogram.Comment: 4 pages, 5 figures, 3 table
Towards Minkowski Vacua in Type II String Compactifications
We study the vacuum structure of compactifications of type II string theories
on orientifolds with SU(3)xSU(3) structure. We argue that generalised geometry
enables us to treat these non-geometric compactifications using a supergravity
analysis in a way very similar to geometric compactifications. We find
supersymmetric Minkowski vacua with all the moduli stabilised at weak string
coupling and all the tadpole conditions satisfied. Generically the value of the
moduli fields in the vacuum is parametrically controlled and can be taken to
arbitrarily large values.Comment: 33 pages; v2 minor corrections, references added, version to appear
in JHE
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