ATP metabolism is controlled mainly by ATP synthase (ATP ase ) and creatine kinase (CK) reactions that regulate cerebral ATP production, transportation, and utilization. These coupled reactions constitute a chemical exchange metabolic network of PCr7ATP7Pi characterized by two forward and two reverse reaction fluxes, which can be studied noninvasively by in vivo 31 P MRS combined with magnetization transfer (MT). However, it is still debated whether current MT approaches can precisely determine all of these fluxes. We developed and tested a modified in vivo 31 P MT approach based on a multiple single-site saturation (MSS) technique to study the entire PCr7ATP7Pi network in human occipital lobe at 7T. Our results reveal that 1) the MSS MT approach can explicitly determine all four reaction fluxes with a minimal number of The primary functions of brain cells are excitation and conduction, which are reflected by constant electrophysiological activity in the brain. The cerebral bioenergetics that support sustained electrophysiological activity are ultimately driven by a variety of biochemical processes that maintain the normal function and structural integrity of the brain (1). Of these processes, the most fundamental for supporting various cellular activities is adenosine triphosphate (ATP) metabolism in living cells (2). The majority of ATP is formed from adenosine diphosphate (ADP) and inorganic phosphate (Pi) in the mitochondria through oxidative phosphorylation catalyzed by the ATP synthase (ATP ase ) enzyme, as illustrated by Fig. 1a (3,4). The highly demanding biochemical processes involving ATP production and utilization in the brain cause rapid chemical cycling among ATP, ADP, and Pi (see Fig. 1a). These processes are also accompanied by another important chemical reaction involving phosphocreatine (PCr) and creatine kinase (CK). PCr acts as an ATP reservoir and carrier, and transfers energy from the mitochondria to sites of ATP utilization in the cytosol through reversible CK reactions, ultimately maintaining a stable cellular ATP level (4,5). These two chemical exchange reactions (i.e., PCr7ATP and Pi7ATP) play central roles in regulating ATP metabolism and maintaining normal ATP functionality, both of which are crucial for cerebral bioenergetics and brain function in the healthy brain as well as in neurodegenerative diseases. Moreover, the ATP ase and CK reactions are tightly coupled together, leading to a complex three-31 P-spin chemical exchange kinetic network (i.e., PCr7ATP7Pi) as depicted in Fig. 1b. Thus, it is essential to develop a noninvasive, reliable technique that is capable of assessing the entire kinetic network of PCr7ATP7Pi and associated ATP metabolic fluxes in situ, particularly in the human brain.Measuring all kinetic parameters involved in the PCr7ATP7Pi network requires extensive information, including three steady-state phosphate metabolite concentrations (i.e., [ATP], [PCr], and [Pi]) and four pseudo-firstorder chemical reaction rate constants (forward and reverse rate constants fo...

Nanostructuring of thermoelectric materials bears promise for manipulating physical parameters to improve the energy conversion efficiency of thermoelectrics. Using nonequilibrium molecular dynamics, we investigate how the thermal conductivity can be altered in core-shell nanocomposites of Si and Ge. By calculating the phonon vibrational density of states and performing normal mode analysis, we show that the thermal conductivity decreases when phonon-transport becomes diffusion-dominated and unveil a competition between modes from the various regions of the nanocomposite (core, interface, and shell). The effects of nanowire length, cross section, and temperature on thermal conductivity are explicitly considered. Surprisingly, the thermal conductivity variation with nanowire length is much weaker than in pure nanowires. Also, the thermal conductivity is almost independent of temperature in the wide region between 50 and 600 K, a direct result of confinement of the core by the shell. These results suggest that core-shell nanowires are promising structures for thermoelectrics.