United States Department of Energy

About: United States Department of Energy is a government organization based out in Washington D.C., District of Columbia, United States. It is known for research contribution in the topics: Coal & Catalysis. The organization has 13656 authors who have published 14177 publications receiving 556962 citations. The organization is also known as: DOE & Department of Energy.

Order- N spectral method for electromagnetic waves

Abstract: We show that the eigenmodes for electromagnetic waves in an inhomogeneous dielectric medium can be obtained with an algorithm that scales linearly with the size of the system. The method employs discretization of the Maxwell equations in both the spatial and the time domain and the integration of the Maxwell equations in the time domain. The spectral intensity can then be obtained by a Fourier transform. We applied the method to a few problems of current interest, including the photonic band structure of a periodic dielectric structure, the effective dielectric constants of some three-dimensional and two-dimensional systems, and the defect states of a periodic dielectric structure with structural defects.

A restricted spectrum of NRAS mutations causes Noonan syndrome

Abstract: Noonan syndrome, a developmental disorder characterized by congenital heart defects, reduced growth, facial dysmorphism and variable cognitive deficits, is caused by constitutional dysregulation of the RAS-MAPK signaling pathway. Here we report that germline NRAS mutations conferring enhanced stimulus-dependent MAPK activation account for some cases of this disorder. These findings provide evidence for an obligate dependency on proper NRAS function in human development and growth.

A precision measurement of the gravitational redshift by the interference of matter waves

Abstract: A central prediction of general relativity states that a gravitational field slows the running of a clock. Previous measurements of this effect, known as gravitational redshift, have involved clocks at different heights, and until now this has been the least accurately determined of the parameters supporting curved space-time theories. Now this prediction has been confirmed to unprecedented accuracy using the results of lab experiments performed more than 10 years ago in a study of the acceleration of free fall. Analysis of the data — on quantum interference of single caesium atoms bobbing up and down in an atomic fountain — provides a measurement based on matter-wave interference that improves accuracy by a factor of 10,000. One of the central predictions of general relativity is that a clock in a gravitational potential well runs more slowly than a similar clock outside the well. This effect, known as gravitational redshift, has been measured using clocks on a tower, an aircraft and a rocket, but here, laboratory experiments based on quantum interference of atoms are shown to produce a much more precise measurement. One of the central predictions of metric theories of gravity, such as general relativity, is that a clock in a gravitational potential U will run more slowly by a factor of 1 + U/c2, where c is the velocity of light, as compared to a similar clock outside the potential1. This effect, known as gravitational redshift, is important to the operation of the global positioning system2, timekeeping3,4 and future experiments with ultra-precise, space-based clocks5 (such as searches for variations in fundamental constants). The gravitational redshift has been measured using clocks on a tower6, an aircraft7 and a rocket8, currently reaching an accuracy of 7 × 10-5. Here we show that laboratory experiments based on quantum interference of atoms9,10 enable a much more precise measurement, yielding an accuracy of 7 × 10-9. Our result supports the view that gravity is a manifestation of space-time curvature, an underlying principle of general relativity that has come under scrutiny in connection with the search for a theory of quantum gravity11. Improving the redshift measurement is particularly important because this test has been the least accurate among the experiments that are required to support curved space-time theories1.