Estimating Betas and Stock-Return Correlations From Monthly Data: A Warning Note.

The empirical finance literature makes extensive use of 'monthly' stock returns, where a monthly return is the change in stock price between one particular day of the calendar month - which we term the reference day - and the corresponding day of the following month. We show that estimates of betas and stock-market correlations are highly sensitive to the choice of reference day and we suggest that studies based on such estimates can be unreliable. We support this claim by carrying out two small-scale empirical studies showing in each case that the results of critical tests are dependent upon the choice of reference day.betas, international correlations, estimation risk

Aerodynamic and acoustic effects of eliminating core swirl from a full scale 1.6 stage pressure ratio fan (QF-5A)

Fan QF-5A was a modification of fan QF-5 which had an additional core stator and adjusted support struts to turn the core exit flow from a 30 deg swirl to the axial direction. This modification was necessary to eliminate the impingement of the swirling core flow on the axial support pylon of the NASA-Lewis Quiet Fan Facility that caused aerodynamic, acoustic and structural problems with the original fan stage at fan speeds greater than 85 percent of design. The redesigned fan QF-5A did obtain the design bypass ratio with an increased core airflow suggesting that the flow problem was resolved. Acoustically, the redesigned stage showed a low frequency broadband noise reduction compared to the results for fan QF-5 at similar operating conditions

Experimental steady-state performance of a multitube, centrally finned, potassium condensing radiator

Steady state performance of multitube, centrally finned, potassium condensing radiato

Natural icing of an axial-flow turbojet engine in flight for a single icing condition

An investigation has been conducted in natural icing conditions to determine the effect of ice formations on the performance of an axial-flow turbojet engine. One flight was made in an icing condition in which the liquid-water content varied from 0.077 to 0.490 gram per cubic meter and the average droplet size varied from 5.4 to 12.1 microns. During a period of 60 minutes in icing, at an engine speed of 11,000 rpm, the tail-pipe temperature increased from 865 degrees to 965 degrees F. and the jet thrust decreased from 1950 to 1700 pounds. Near the end of the icing period, the engine was satisfactorily accelerated to take-off power