Proceedings of the National Academy of Sciences (PNAS)

Could dark energy be changing over time?

Einstein’s version of dark energy is known as the cosmological constant. It implies a fixed amount of dark energy in each ...
PNAS

DNA-nanotube-induced alignment of membrane proteins for NMR structure determination

The general applicability of solution NMR spectroscopy to structural characterization of intact α-helical membrane proteins has been demonstrated by a number of recent studies. Examples include the ...
PNAS

Front Matter

Dive into PNAS Front Matter for editorials, interviews, science news, and commentary that offer expert perspective on today’s most important research findings.
PNAS

Solving the apparent diversity-accuracy dilemma of recommender systems

Recommender systems use data on past user preferences to predict possible future likes and interests. A key challenge is that while the most useful individual recommendations are to be found among ...
PNAS

Phonon softening and crystallographic orientation of strained graphene studied by Raman spectroscopy

We present a systematic study of the Raman spectra of optical phonons in graphene monolayers under tunable uniaxial tensile stress. Both the G and 2D bands exhibit significant red shifts. The G band ...
PNAS

US particulate matter air quality improves except in wildfire-prone areas

Wildfires are a major source of fine particulate matter (diameter <2.5 µm; PM 2.5), which is a health hazard. Since the mid-1980s, the total US area burned by wildfires has been increasing, with fires ...
PNAS

Superconductive sodalite-like clathrate calcium hydride at high pressures

Edited by Michael L. Klein, Temple University, Philadelphia, PA, and approved February 17, 2012 (received for review November 5, 2011) ...
PNAS

Soil warming, carbon–nitrogen interactions, and forest carbon budgets

Soil warming has the potential to alter both soil and plant processes that affect carbon storage in forest ecosystems. We have quantified these effects in a large, long-term (7-y) soil-warming study ...
PNAS

The water footprint of humanity

Edited by Peter H. Gleick, Pacific Institute for Studies in Development, Environment, and Security, Oakland, CA, and approved December 21, 2011 (received for review June 20, 2011) In formulating ...
PNAS

Quantum heat engine power can be increased by noise-induced coherence

Open in Viewer (A) Schematic of a photocell consisting of quantum dots sandwiched between p and n doped semiconductors. Open circuit voltage and solar photon energy ℏνh are related by the Carnot ...
PNAS

Non-blinking and photostable upconverted luminescence from single lanthanide-doped nanocrystals

Photostability and non-blinking behavior of a single UCNP. (A) The time trace of emission intensity from a single UCNP under continuous laser illumination for more than 1 h, suggesting the durable ...
PNAS

Evidence for van der Waals adhesion in gecko setae

Geckos have evolved one of the most versatile and effective adhesives known. The mechanism of dry adhesion in the millions of setae on the toes of geckos has been the focus of scientific study for ...