PNAS | January 17, 2006 | vol. 103 | no. 3 | 505-506
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This Week in PNAS
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ASTRONOMY
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Numerical relativity in complex plane
Maurice van Putten proposes an alternative approach to numerical relativity by working in the complex plane. Efficient and stable computational algorithms for numerical relativity can aid in the analysis of gravitational-wave emissions data, which are important in the search for coalescing black holes. However, singularities associated with black hole spacetimes present challenges for calculating bursts and preceding chirps over many wave periods. Here, van Putten instead turns to spectral methods and focuses on the bursts of radiation produced by binary black hole coalescence that propagate toward quiescent infinity. This approach circumvents spacetime singularities, includes infinity, and avoids the need to impose radiative boundary conditions. The author uses three-dimensional spectral representations with spherical harmonics in the angular coordinates and Fourier series in a complex radial coordinate. The result creates an efficient representation of black hole spacetimes and, compared with the standard finite differencing approaches, offers a reduction in computational effort by orders of magnitude. The author applied this theory to Boyer–Lindquist initial data of two black holes, additionally illustrated with a scalar wave equation with signal recovery by Cauchy's integral formula. — R.N.
"Global spectral representations of black hole spacetimes in the complex plane" by Maurice H. P. M. van Putten (see pages 519–522)
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ECOLOGY
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Global patterns of soil bacterial biodiversity
According to Noah Fierer and Robert Jackson, soil pH is the best predictor of soil bacterial diversity and richness. Using ribosomal DNA fingerprinting, Fierer and Jackson compared the community composition of 98 soil samples from across North and South America to examine which factors influence biodiversity on a continental scale. The authors found that the variables associated with plant and animal diversity, such as mean temperature, latitude, and potential evapotranspiration, do not affect bacterial diversity. Rather, soil pH is the most important variable at a global level, with neutral pH soils being the most diverse and diversity decreasing as acidity rises. Soil pH is also the best predictor of overall community composition, whereas geographic distance does not relate strongly to composition, because forests in the northeast and northwest United States with similar environmental characteristics have similar microbe communities. This study suggests that the biogeographical patterns of soil bacteria are fundamentally distinct from those of macroorganisms, best exemplified by the finding that the Amazon, one of the richest centers of plant and animal diversity, actually has one of the least diverse soil bacteria communities in the Americas because of its acidic soil. — N.Z.
"The diversity and biogeography of soil bacterial communities" by Noah Fierer and Robert B. Jackson (see pages 626–631)
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GENETICS
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Enzyme's role in familial erythrocytosis
Melanie Percy et al. report that familial erythrocytosis may be caused by a mutation in the prolyl hydroxylase domain 2 (PHD2) enzyme. Familial erythrocytosis is a rare disease in which individuals overproduce red blood cells. Previous research has shown that, under low oxygen conditions, prolyl hydroxylase domain proteins are less able to hydroxylate the 
-subunit of hypoxia-inducible factor (HIF), resulting in reduced degradation of HIF. HIF binds to hypoxia response elements and activates the Epo gene, which controls red blood cell production. Percy et al. sequenced DNA from a family in which the father and two children had familial erythrocytosis, with elevated hemoglobin levels. All three individuals possessed a change in the coding region of PHD2, at an evolutionarily conserved proline residue. The hematologically normal mother of the family did not have this mutation. No changes in the coding regions of other PHD genes or that of HIF-1 were observed.
In vitro, mutant PHD2 bound weakly to HIF-1 and HIF-2 and displayed a decreased ability to hydroxylate HIF compared with wild-type enzyme. — F.A.
"A family with erythrocytosis establishes a role for prolyl hydroxylase domain protein 2 in oxygen homeostasis" by Melanie J. Percy, Quan Zhao, Adrian Flores, Claire Harrison, Terence R. J. Lappin, Patrick H. Maxwell, Mary Frances McMullin, and Frank S. Lee (see pages 654–659)
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NEUROSCIENCE
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Etching memories via activity shifts
Atsuko Takashima et al. report that shifts in brain activity and deep sleep may help memories become permanent. Although recall of recent memories relies on the hippocampus, retrieval of older memories can be sustained by cortical activation alone. Evidence of a system-level reorganization of this activity has not been directly observed. Takashima et al. used functional MRI to monitor brain activity changes during memory consolidation and correlated this activity with duration of slow-wave sleep, the deepest sleep phase. Subjects memorized a series of landscape photographs, napped, and were presented with new images. The subjects were then tested in their ability to recognize "old" versus "recent" images at 1, 2, 30, and 90 days after the initial exposure. Retrieval-associated hippocampal activity was found to decrease over time, with the ventral medial prefrontal cortex gradually increasing activity over the testing period. Additionally, subjects who experienced more slow-wave sleep had stronger changes in brain activity and improved retrieval. The results support the theory that memory consolidation is promoted by slow-wave sleep and involves a gradual takeover of hippocampal processing by the neocortex. — M.M.
"Declarative memory consolidation in humans: A prospective functional magnetic resonance imaging study" by A. Takashima, K. M. Petersson, F. Rutters, I. Tendolkar, O. Jensen, M. J. Zwarts, B. L. McNaughton, and G. Fernández (see pages 756–761)
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Related articles in PNAS:
- From the Cover: Global spectral representations of black hole spacetimes in the complex plane
- Maurice H. P. M. van Putten
PNAS 2006 103: 519-522.
[Abstract]
[Full Text]
- From the Cover: The diversity and biogeography of soil bacterial communities
- Noah Fierer and Robert B. Jackson
PNAS 2006 103: 626-631.
[Abstract]
[Full Text]
- From the Cover: A family with erythrocytosis establishes a role for prolyl hydroxylase domain protein 2 in oxygen homeostasis
- Melanie J. Percy, Quan Zhao, Adrian Flores, Claire Harrison, Terence R. J. Lappin, Patrick H. Maxwell, Mary Frances McMullin, and Frank S. Lee
PNAS 2006 103: 654-659.
[Abstract]
[Full Text]
- From the Cover: Declarative memory consolidation in humans: A prospective functional magnetic resonance imaging study
- A. Takashima, K. M. Petersson, F. Rutters, I. Tendolkar, O. Jensen, M. J. Zwarts, B. L. McNaughton, and G. Fernández
PNAS 2006 103: 756-761.
[Abstract]
[Full Text]
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