How to make maps from CMB data without losing information

The next generation of CMB experiments can measure cosmological parameters with unprecedented accuracy - in principle. To achieve this in practice when faced with such gigantic data sets, elaborate data analysis methods are needed to make it computationally feasible. An important step in the data pipeline is to make a map, which typically reduces the size of the data set my orders of magnitude. We compare ten map-making methods, and find that for the Gaussian case, both the method used by the COBE DMR team and various variants of Wiener filtering are optimal in the sense that the map retains all cosmological information that was present in the time-ordered data (TOD). Specifically, one obtains just as small error bars on cosmological parameters when estimating them from the map as one could have obtained by estimating them directly from the TOD. The method of simply averaging the observations of each pixel (for total-power detectors), on the contrary, is found to generally destroy information, as does the maximum entropy method and most other non-linear map-making techniques. Since it is also numerically feasible, the COBE method is the natural choice for large data sets. Other lossless (e.g. Wiener-filtered) maps can then be computed directly from the COBE method map.Comment: Minor revisions to match published version. 12 pages, with 1 figure included. Color figure and links at http://www.sns.ias.edu/~max/mapmaking.html (faster from the US), from http://www.mpa-garching.mpg.de/~max/mapmaking.html (faster from Europe) or from [email protected]

Linguistics Landscape: a Cross Culture Perspective

This paper was to aim in discussing the linguistic landscape. It was the visibility and salience of languages on public and commercial signs in a given territory or region (Landry and Bourhis 1997). The linguistic landscape has been described as being somewhere at the junction of sociolinguistics, sociology, social psychology, geography, and media studies. It is a concept used in sociolinguistics as scholars study how languages are visually used in multilingual societies, from large metropolitan centers to Amazonia. For example, some public signs in Jerusalem are in Hebrew, English, and Arabic (Spolsky and Cooper 1991, Ben-Rafael et al., 2006). Studies of the linguistic landscape have been published from research done around the world. The field of study is relatively recent; the linguistic landscape paradigm has evolved rapidly and while it has some key names associated with it, it currently has no clear orthodoxy or theoretical core

Model Tests on the Economy and Effectiveness of Helicopter Propellers

The average velocity of helicopter blades relative to the air is greater than that of airplane wings. The helicopter may turn out to be more economical than the airplane wing for extreme velocities of horizontal flight, the airplane then requiring a very great speed range

Notes on propeller design IV : general proceeding in design

The choice of the numbers of revolutions and of the diameter, the distribution of thrust, and the values of the constants in the aerodynamical equations of the propeller are discussed

Elements of the Wing Section Theory and of the Wing Theory

Results are presented of the theory of wings and of wing sections which are of immediate practical value. They are proven and demonstrated by the use of the simple conceptions of kinetic energy and momentum only

Remarks on the Pressure Distribution over the Surface of an Ellipsoid, Moving Translationally Through a Perfect Fluid

This note, prepared for the National Advisory Committee for Aeronautics, contains a discussion of the pressure distribution over ellipsoids when in translatory motion through a perfect fluid. An easy and convenient way to determine the magnitude of the velocity and of the pressure at each point of the surface of an ellipsoid of rotation is described. The knowledge of such pressure distribution is of great practical value for the airship designer. The pressure distribution over the nose of an airship hull is known to be in such good agreement with the theoretical distribution as to permit basing the computation of the nose stiffening structure on the theoretical distribution of pressure

Note on vortices on their relation to the lift of airfoils

This note, prepared for the NACA, contains a discussion of the meaning of vortices, so often mentioned in connection with the creation of lift by wings. The action of wings can be more easily understood without the use of vortices

The twisted wing with elliptic plan form

A method for computing the aerodynamic induction of wings with elliptic plan form if arbitrarily twisted

The velocity distribution caused by an airplane at the points of a vertical plane containing the span

A formula for the computation of the vertical velocity component on all sides of an airplane is deduced and discussed. The formation is of value for the interpretation of such free flight tests where two airplanes fly alongside each other to facilitate observation

Notes on aerodynamic forces II : curvilinear motion

The laws of curvilinear motion are established and the transverse forces on elongated airship hulls along a curved path are investigated