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Conventional design of wireless networks mainly focuses on system capacity and spectral efficiency (SE). As green radio (GR) becomes an inevitable trend, energy-efficient design in wireless networks is becoming more and more important. In this paper, the fundamental relation between energy efficiency (EE) and SE in downlink orthogonal frequency division multiple access (OFDMA) networks is addressed. We first set up a general EE-SE tradeoff framework, where the overall EE, SE and peruser quality-of-service (QoS) are all considered, and prove that EE is strictly quasiconcave in SE. We also find a tight upper bound and a tight lower bound on the EE-SE curve for general scenarios, which reflect the actual EE-SE relation. We then focus on a special case that priority and fairness are considered and develop a low-complexity but near-optimal resource allocation algorithm for practical application of the EE-SE tradeoff. Numerical results corroborate the theoretical findings and demonstrate the effectiveness of the proposed resource allocation scheme for achieving a flexible and desirable tradeoff between EE and SE.Index Terms-Energy efficiency (EE), green radio (GR), orthogonal frequency division multiple access (OFDMA), spectral efficiency (SE) *

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Mammalian H3.3 is a variant of the canonical histone H3.1 essential for genome reprogramming in the fertilized eggs and maintenance of chromatin structure in neuronal cells. An H3.3-specific histone chaperone, DAXX, directs the deposition of H3.3 onto pericentric and telomeric heterochromatin. H3.3 differs from H3.1 by only five amino acids, yet DAXX can distinguish the two with high precision. By a combination of structural, biochemical and cell-based targeting analyses, here we show that Ala87 and Gly90 are the principal determinants of H3.3 specificity. DAXX uses a shallow hydrophobic pocket to accommodate the small, hydrophobic Ala87 of H3.3, whereas a polar binding environment in DAXX prefers Gly90 in H3.3 over the hydrophobic Met90 in H3.1. An H3.3-H4 heterodimer is bound by the histone-binding domain of DAXX, which makes extensive contacts with both H3.3 and H4.