Showing papers by "Queen Mary University of London published in 2001"

A mouse Mecp2-null mutation causes neurological symptoms that mimic rett syndrome

Abstract: Rett syndrome (RTT) is an inherited neurodevelopmental disorder of females that occurs once in 10,000-15,000 births. Affected females develop normally for 6-18 months, but then lose voluntary movements, including speech and hand skills. Most RTT patients are heterozygous for mutations in the X-linked gene MECP2 (refs. 3-12), encoding a protein that binds to methylated sites in genomic DNA and facilitates gene silencing. Previous work with Mecp2-null embryonic stem cells indicated that MeCP2 is essential for mouse embryogenesis. Here we generate mice lacking Mecp2 using Cre-loxP technology. Both Mecp2-null mice and mice in which Mecp2 was deleted in brain showed severe neurological symptoms at approximately six weeks of age. Compensation for absence of MeCP2 in other tissues by MeCP1 (refs. 19,20) was not apparent in genetic or biochemical tests. After several months, heterozygous female mice also showed behavioral symptoms. The overlapping delay before symptom onset in humans and mice, despite their profoundly different rates of development, raises the possibility that stability of brain function, not brain development per se, is compromised by the absence of MeCP2.

Local Reasoning about Programs that Alter Data Structures

Abstract: We describe an extension of Hoare's logic for reasoning about programs that alter data structures. We consider a low-level storage model based on a heap with associated lookup, update, allocation and deallocation operations, and unrestricted address arithmetic. The assertion language is based on a possible worlds model of the logic of bunched implications, and includes spatial conjunction and implication connectives alongside those of classical logic. Heap operations are axiomatized using what we call the "small axioms", each of which mentions only those cells accessed by a particular command. Through these and a number of examples we show that the formalism supports local reasoning: A specification and proof can concentrate on only those cells in memory that a program accesses. This paper builds on earlier work by Burstall, Reynolds, Ishtiaq and O'Hearn on reasoning about data structures.

Bone marrow contributes to renal parenchymal turnover and regeneration

Abstract: In order to establish whether extra-renal cells contribute to the turnover and repair of renal tissues, this study examined kidneys of female mice that had received a male bone marrow transplant and kidney biopsies from male patients who had received kidney transplants from female donors. By using in situ hybridization to detect Y-chromosomes it could be demonstrated that circulating stem cells frequently engraft into the kidney and differentiate into renal parenchymal cells. In the human renal grafts it was confirmed that some of the recipient-derived cells within the kidney exhibited a tubular epithelial phenotype, by combining in situ hybridization with immunostaining for the epithelial markers CAM 5.2 and the lectin Ulex europaeus. Female mouse recipients of male bone marrow grafts showed co-localization of Y-chromosomes and tubular epithelial markers Ricinus communis and Lens culinaris, and a specific cytochrome P450 enzyme (CYP1A2) indicating an appropriate functional capability of clustered newly formed marrow-derived tubular epithelial cells. Y-chromosome-containing cells were observed within glomeruli, with morphology and location appropriate for podocytes. Within the murine kidney, these Y-chromosome-positive cells were negative for the mouse macrophage marker F4/80 antigen and leukocyte common antigen, but were vimentin-positive. The presence of bone marrow-derived cells was noted in both histologically normal mouse kidneys and in human transplanted kidneys suffering damage from a variety of causes. These data indicate that bone marrow cells contribute to both normal turnover of renal epithelia and regeneration after damage, and it is suggested that this could be exploited therapeutically.

Gene trees and species trees are not the same

Abstract: The relationship between species is usually represented as a bifurcating tree with the branching points representing speciation events. The ancestry of genes taken from these species can also be represented as a tree, with the branching points representing ancestral genes. The time back to the branching points, and even the branching order, can be different between the two trees. This possibility is widely recognized, but the discrepancies are often thought to be small. A different picture is emerging from new empirical evidence, particularly that based on multiple loci or on surveys with a wide geographical scope. The discrepancies must be taken into account when estimating the timing of speciation events, especially the more recent branches. On the positive side, the different timings at different loci provide information about the ancestral populations.

BI as an assertion language for mutable data structures

Abstract: Reynolds has developed a logic for reasoning about mutable data structures in which the pre- and postconditions are written in an intuitionistic logic enriched with a spatial form of conjunction. We investigate the approach from the point of view of the logic BI of bunched implications of O'Hearnand Pym. We begin by giving a model in which the law of the excluded middleholds, thus showing that the approach is compatible with classical logic. The relationship between the intuitionistic and classical versions of the system is established by a translation, analogous to a translation from intuitionistic logic into the modal logic S4. We also consider the question of completeness of the axioms. BI's spatial implication is used to express weakest preconditions for object-component assignments, and an axiom for allocating a cons cell is shown to be complete under an interpretation of triplesthat allows a command to be applied to states with dangling pointers. We make this latter a feature, by incorporating an operation, and axiom, for disposing of memory. Finally, we describe a local character enjoyed by specifications in the logic, and show how this enables a class of frame axioms, which say what parts of the heap don't change, to be inferred automatically.

Cosmology from MAXIMA-1, BOOMERANG, and COBE DMR cosmic microwave background observations.

Abstract: Recent results from BOOMERANG-98 and MAXIMA-1, taken together with COBE DMR, provide consistent and high signal-to-noise measurements of the cosmic microwave background power spectrum at spherical harmonic multipole bands over 2

Neuropathology of inflicted head injury in children. I. Patterns of brain damage.

Abstract: Fifty-three cases of non-accidental head injury in children were subjected to detailed neuropathological study, which included immunocytochemistry for microscopic damage. Clinical details were available for all the cases. There were 37 infants, age at head injury ranging from 20 days to 9 months, and 16 children (range 13 months to 8 years). The most common injuries were skull fractures (36% of cases), acute subdural bleeding (72%) and retinal haemorrhages (71%); the most usual cause of death was raised intracranial pressure secondary to brain swelling (82%). On microscopy, severe hypoxic brain damage was present in 77% of cases. While vascular axonal damage was found in 21 out of 53 cases, diffuse traumatic axonal injury was present in only three. Eleven additional cases, all of them infants, showed evidence of localized axonal injury to the craniocervical junction or the cervical cord. When the data were analysed by median age at head injury, statistically significant patterns of age-related damage emerged. Our study shows that infants of 2-3 months typically present with a history of apnoea or other breathing abnormalities, show axonal damage at the craniocervical junction, and tend also to have a skull fracture, a thin film of subdural haemorrhage, but lack extracranial injury. Children over 1 year are more likely to suffer severe extracranial, particularly abdominal, injuries. They tend to have larger subdural haemorrhages, and where traumatic axonal injury is present, show patterns of hemispheric white matter damage more akin to those reported in adults. Diffuse axonal injury is an uncommon sequel of inflicted head injury in children.

Cost-effectiveness analysis and the consistency of decision making: evidence from pharmaceutical reimbursement in australia (1991 to 1996).

Abstract: Objective: The principle aim of this study was to generate a league table of drugs considered by the Australian Pharmaceutical Benefits Advisory Committee (PBAC) for reimbursement. The table was used to test the hypothesis that decisions made by the PBAC are consistent with the maxim of economic efficiency. In addition, we explored whether the past decisions by the PBAC revealed a threshold incremental cost-effectiveness ratio beyond which the PBAC is not prepared to recommend reimbursement of a drug. Methods: All 355 submissions made to the PBAC between January 1991 and June 1996 were reviewed. Submissions using cost per life-year gained (26 submissions) or the cost per quality adjusted life-year (QALY) gained (9 submissions) were ranked in a league table and compared with advice given by the PBAC about that drug. The confidentiality restrictions for the submissions require that the individual drug details cannot be revealed in this article. Results: There was a statistically significant difference between the cost per life-year gained for drugs that were recommended for listing and those that were not, suggesting that the PBAC has been broadly consistent with the use of economic efficiency as a criterion for decision making. We did not find an explicit threshold beyond which the PBAC was unwilling to pay for additional life years gained. However, between 1992 and 1996 the PBAC appears to have been unlikely to recommend a drug for listing if the additional cost per life-year exceeded 76 000 Australian dollars [$AU] (1998/1999 values) and was unlikely to reject a drug for which the additional cost per life-year gained was less than $AU42 000. The cost-effectiveness ratio was not the only factor determining the reimbursement decision. Conclusions: The results of this preliminary study indicate that decisions to recommend a drug for listing by the PBAC in the last few years have, by and large, been consistent with the notion of economic efficiency.

The neurobiology and evolution of cannabinoid signalling

Abstract: The plant Cannabis sativa has been used by humans for thousands of years because of its psychoactivity. The major psychoactive ingredient of cannabis is Delta(9)-tetrahydrocannabinol, which exerts effects in the brain by binding to a G-protein-coupled receptor known as the CB1 cannabinoid receptor. The discovery of this receptor indicated that endogenous cannabinoids may occur in the brain, which act as physiological ligands for CB1. Two putative endocannabinoid ligands, arachidonylethanolamide ('anandamide') and 2-arachidonylglycerol, have been identified, giving rise to the concept of a cannabinoid signalling system. Little is known about how or where these compounds are synthesized in the brain and how this relates to CB1 expression. However, detailed neuroanatomical and electrophysiological analysis of mammalian nervous systems has revealed that the CB1 receptor is targeted to the presynaptic terminals of neurons where it acts to inhibit release of 'classical' neurotransmitters. Moreover, an enzyme that inactivates endocannabinoids, fatty acid amide hydrolase, appears to be preferentially targeted to the somatodendritic compartment of neurons that are postsynaptic to CB1-expressing axon terminals. Based on these findings, we present here a model of cannabinoid signalling in which anandamide is synthesized by postsynaptic cells and acts as a retrograde messenger molecule to modulate neurotransmitter release from presynaptic terminals. Using this model as a framework, we discuss the role of cannabinoid signalling in different regions of the nervous system in relation to the characteristic physiological actions of cannabinoids in mammals, which include effects on movement, memory, pain and smooth muscle contractility. The discovery of the cannabinoid signalling system in mammals has prompted investigation of the occurrence of this pathway in non-mammalian animals. Here we review the evidence for the existence of cannabinoid receptors in non-mammalian vertebrates and invertebrates and discuss the evolution of the cannabinoid signalling system. Genes encoding orthologues of the mammalian CB1 receptor have been identified in a fish, an amphibian and a bird, indicating that CB1 receptors may occur throughout the vertebrates. Pharmacological actions of cannabinoids and specific binding sites for cannabinoids have been reported in several invertebrate species, but the molecular basis for these effects is not known. Importantly, however, the genomes of the protostomian invertebrates Drosophila melanogaster and Caenorhabditis elegans do not contain CB1 orthologues, indicating that CB1-like cannabinoid receptors may have evolved after the divergence of deuterostomes (e.g. vertebrates and echinoderms) and protostomes. Phylogenetic analysis of the relationship of vertebrate CB1 receptors with other G-protein-coupled receptors reveals that the paralogues that appear to share the most recent common evolutionary origin with CB1 are lysophospholipid receptors, melanocortin receptors and adenosine receptors. Interestingly, as with CB1, each of these receptor types does not appear to have Drosophila orthologues, indicating that this group of receptors may not occur in protostomian invertebrates. We conclude that the cannabinoid signalling system may be quite restricted in its phylogenetic distribution, probably occurring only in the deuterostomian clade of the animal kingdom and possibly only in vertebrates.

A Procedure for Isolating Soil Organic Matter Fractions Suitable for Modeling

Abstract: defined by their rate of decomposition. Hence fraction i is defined as obeying: Fractions of soil organic matter (SOM) were obtained from three soils using alternative physical fractionation procedures, and evaluated i kiYi [1] against the requirements of model pools. We compared two-stage where i is the mineralization rate of fraction i; ki is its density fractionation (isolating free and intra-aggregate fractions, befirst order reactivity; and Yi is its size. Cohort models fore and after dispersion, respectively) with particle-size separation of dispersed soil. For full comparison, the organomineral fraction (Bosatta and A u gren, 1996) are conceptually different residual from density fractionation was also size separated. In stand- from the approach described above. However, they are ardizing the density-based method, we found recovery of intra-aggre- similar mathematically, and may be considered as modgate organic matter highly sensitive to separation density as compared els whose multiple pools encompass a sufficient range with the free. Recovery of the intra-aggregate was also influenced by of reactivity (ki). dispersion energy. The greatest amount was obtained using a combina- Measurements of system-level outputs, such as total

Effects of environmental conditions on mechanical and physical properties of flax fibers

Abstract: The environmental degradation behaviour of flax fibers and their mechanical properties were investigated Upgraded Duralin flax fibers, which have been treated by a novel treatment process for improved moisture and rot sensitivity, were studied Results showed that upgraded Duralin flax fibers absorbed less moisture than untreated Green flax fibers, whereas the mechanical properties of the upgraded fibers were retained with moisture absorption, if not improved In addition electrochemical studies were conducted on these fibers These data agreed well with conventional moisture absorption data Zeta (ζ)-potential measurements at different pH-levels showed differences for Duralin fibers, which can be attributed to differences in morphological features

Effect of sodium hypochlorite on mechanical properties of dentine and tooth surface strain

Abstract: Aim The aim of this study was to test the null hypothesis that sodium hypochlorite irrigation of root canals dues not alter the properties of dentine and contribute to the weakening of root-treated teeth.Methodology The effect of two concentrations (0.5%, 5.25%) of sodium hypochlorite (NaOCl) and saline on ii) the elastic modulus and flexural strength of machined dentine bars, and (ii) changes in strain of 'whole' extracted human teeth were evaluated. One hundred standardized piano-parallel dentine bars (> 11.7 x 0.8 x 0.8 mm) were randomly divided into the three groups, immersed for 2 h in the respective solutions and then subjected to a three-point bend test. Changes in strain of each of 10 teeth on cyclical nondestructive occlusal loading were measured using electrical resistance strain gauges bonded to the cervical aspects. Each tooth had its crown and enamel reduced and root canal prepared. These were irrigated sequentially in a series of four separate, 30-minute regimes; initial-saline, 0.5% NaOCl, 5.25% NaOCl and final-saline. The changes in strains after each irrigation regime were compared.Results There was a significant decrease in elastic modulus of the dentine bars immersed in 5.25% NaOCl compared with the saline group (P < 0.01). There was also a significant decrease in flexural strength of the dentine bars in the 5.25% NaOCl group compared to both the saline and 0.5% NaOCl groups (P < 0.01). The strain data from the nondestructive tooth loading tests revealed significant increases in tensile strain between the initial-saline and the final-saline stages (P<0.01). Significant increases in compressive strains were also found between initial-saline and 5.25% NaOCl; and between 0.5% NaOCl and 5.25% NaOCl stages (P < 0.01).Conclusions The null hypothesis was rejected, 5.25% NaOCl reduced the elastic modulus and flexural strength of dentine. Irrigation of root canals of single, mature rooted premolars with 5.25% NaOCl affected their properties sufficiently to alter their strain characteristics when no enamel was present.

Gut content analysis and a new feeding group classification of termites

Abstract: Summary 1. Gut content analysis of termites was undertaken using microscopical techniques. The 46 study species covered the entire range of taxonomic and feeding forms within the Order. 2. Inter-specific gut contents data were analysed using principal components analysis, placing species along a clear humification gradient based on variations in the amount of silica and plant tissue fragments in the gut. 3. Redundancy analysis was used to find morphological correlates of the observed variation in gut contents. A total of 22 morphological characters (out of 45 candidate characters) were correlated significantly with the gut contents. 4. Three of the 22 significantly correlated characters unambiguously defined feeding groups, which were designated groups I to IV in increasing order of humification of the feeding substrate. Group I contains lower termite dead wood and grass-feeders; group II contains Termitidae with a range of feeding habits including dead wood, grass, leaf litter, and micro-epiphytes; group III contains Termitidae feeding in the organic rich upper layers of the soil; group IV contains the true soil-feeders (again all Termitidae), ingesting apparently mineral soil. These groupings were generally supported statistically in a canonical covariance analysis, although group II apparently represents termite species with a rather wide range of feeding habits. 5. Using existing hypotheses of termite phylogenetic relationships, it seems probable that group I feeders are phylogenetically basal, and that the other groupings have arisen independently on a number of occasions. Soil-feeding (i.e. group III and group IV feeding) may have evolved due to the co-option of faecal material as a fungal substrate by Macrotermitinae-like ancestral forms. As a consequence, these forms would have been constrained to build nest structures from soil and would therefore have passed at least some soil through their guts.

Performance of a new pubertal self-assessment questionnaire: a preliminary study.

Abstract: We describe the performance of a new, self-assessment questionnaire that aims to measure pubertal status by using gender-specific line drawings of the Tanner puberty stages. The study was carried out on 103 children aged 12-16 years attending a paediatric endocrinology outpatient clinic and used physical examination by clinic doctors as the 'gold standard'. Of 133 consecutive, eligible children, 108 (81%) agreed to participate in the study. Data were collected from 62 (60%) males and 41 (40%) females. Mean age was 14.78 years (SD = 1.26 years, range 12.08-16.98 years). For the pubic hair distribution Tanner stage, there was agreement to within one Tanner stage for 90 children (88%), weighted kappa statistic for inter-rater agreement = 0.68 [95% CI 0.49,0.87]. For the female breast/male genitalia Tanner stage, there was agreement to within one Tanner stage for 75 children (76%), kappa = 0.48 [95% CI 0.31,0.64]. The children tended to underestimate their stage of pubertal development. Overall, the kappa statistics implied good agreement for the pubic hair question and moderate agreement for the breast/genitalia stage question in both girls and boys. The questionnaire may prove useful in situations such as large-scale epidemiological studies, in which direct examination of children to determine pubertal status is not possible, and further validation in normal adolescents is warranted.

Feedback control of the rate of peat formation

Abstract: The role of peatlands in the global carbon cycle is confounded by two inconsistencies. First, peatlands have been a large reservoir for carbon sequestered in the past, but may be either net sources or net sinks at present. Second, long-term rates of peat accumulation (and hence carbon sequestration) are surprisingly steady, despite great variability in the short-term rates of peat formation. Here, we present a feedback mechanism that can explain how fine-scale and short-term variability in peat-forming processes is constrained to give steady rates of peat accumulation over longer time-scales. The feedback mechanism depends on a humpbacked relationship between the rate of peat formation and the thickness of the aerobic surface layer (the acrotelm), such that individual microforms (hummocks, lawns, hollows and pools) expand or contract vertically in response to fluctuations in the position of the water table. Hummocks (but not hollows) 'evolve' to a steady state where changes in acrotelm thickness compensate for climate-mediated variations in surface wetness. With long-term growth of a topographically confined peat deposit, the steady state gradually shifts to a thicker acrotelm (i.e. taller hummocks) and lower rates of peat formation and carbon sequestration.

A High Spatial Resolution Analysis of the MAXIMA-1 Cosmic Microwave Background Anisotropy Data

Abstract: We extend the analysis of the MAXIMA-1 cosmic microwave background data to smaller angular scales. MAXIMA, a bolometric balloon-borne experiment, mapped a 124 deg2 region of the sky with 10' resolution at frequencies of 150, 240, and 410 GHz during its first flight. The original analysis, which covered the multipole range 36 ≤ l ≤ 785 using a 100 deg2 map, is extended to l = 1235 using a subset of the data from three 150 GHz photometers in the fully cross-linked central 60 deg2 of the map. The main improvement over the original analysis is the use of 3' square pixels in the calculation of the map. The new analysis is consistent with the original for l 785, where inflationary models predict a third acoustic peak, the new analysis shows power with an amplitude of 56 ± 7 μK at l 850 in excess to the average power of 42 ± 3 μK in the range 441 < l < 785.

Neuropathology of inflicted head injury in children. II. Microscopic brain injury in infants.

Abstract: There are very few reports in the literature dealing with the neuropathology of infant head injury, and the question of whether diffuse traumatic brain damage [diffuse axonal injury (DAI)] occurs in such children has not yet been reliably established by detailed neuropathological studies. We report the findings in the brains of a series of 37 infants aged 9 months or less, all of whom died from inflicted head injuries, and 14 control infants who died of other causes. Axonal damage was identified using immunohistochemistry for beta-amyloid precursor protein. Full clinical details were available for each case, the most constant of which in the study cohort was an episode of significant apnoea at presentation, found to have been recorded in 75% of cases. Global hypoxic damage was the most common histological finding. Widespread axonal damage, interpreted as vascular, was present in 13 cases, but widespread traumatic axonal injury was found in only two children, both of whom had severe head injuries with multiple skull fractures. Epidural cervical haemorrhage and focal axonal damage to the brainstem and the spinal nerve roots, found in 11 cases but not in controls, indicate that the craniocervical junction is vulnerable in infant head injury, the neuropathology being that of stretch injury from cervical hyperextension/flexion. Damage to this region could account for the observed apnoea, which could in turn lead to hypoxic damage and brain swelling. The observation that the predominant histological abnormality in cases of inflicted head injury in the very young is diffuse hypoxic brain damage, not DAI, can be explained in one of two ways: either the unmyelinated axon of the immature cerebral hemispheres is relatively resistant to traumatic damage, or in shaking-type injuries the brain is not exposed to the forces necessary to produce DAI.

Chronic aircraft noise exposure, stress responses, mental health and cognitive performance in school children.

Abstract: Background. Previous research suggests that children are a high risk group vulnerable to the effects of chronic noise exposure. However, questions remain about the nature of the noise effects and the underlying causal mechanisms. This study addresses the effects of aircraft noise exposure on children around London Heathrow airport, in terms of stress responses, mental health and cognitive performance. The research also focuses on the underlying causal mechanisms contributing to the cognitive effects and potential confounding factors.Methods. The cognitive performance and health of 340 children aged 8–11 years attending four schools in high aircraft noise areas (16h outdoor Leq>66dBA) was compared with children attending four matched control schools exposed to lower levels of aircraft noise (16h outdoor Leq<57dBA). Mental health and cognitive tests were group administered to the children in the schools. Salivary cortisol was measured in a subsample of children.Results. Chronic aircraft noise exposure was associated with higher levels of noise annoyance and poorer reading comprehension measured by standardized scales with adjustments for age, deprivation and main language spoken. Chronic aircraft noise was not associated with mental health problems and raised cortisol secretion. The association between aircraft noise exposure and reading comprehension could not be accounted for by the mediating role of annoyance, confounding by social class, deprivation, main language or acute noise exposure.Conclusions.These results suggest that chronic aircraft noise exposure is associated with impaired reading comprehension and high levels of noise annoyance but not mental health problems in children.

Cosmological parameters from the first results of Boomerang

Abstract: The anisotropy of the cosmic microwave background radiation contains information about the contents and history of the universe. We report new limits on cosmological parameters derived from the angular power spectrum measured in the first Antarctic flight of the Boomerang experiment. Within the framework of models with adiabatic perturbations, and using only weakly restrictive prior probabilities on the age of the universe and the Hubble expansion parameter h, we find that the curvature is consistent with flat and that the primordial fluctuation spectrum is consistent with scale invariant, in agreement with the basic inflation paradigm. We find that the data prefer a baryon density Ωbh2 above, though similar to, the estimates from light element abundances and big bang nucleosynthesis. When combined with large scale structure observations, the Boomerang data provide clear detections of both dark matter and dark energy contributions to the total energy density Ωtot, independent of data from high-redshift supernovae.

Reversing type II migration: resonance trapping of a lighter giant protoplanet

Abstract: We present a mechanism related to the migration of giant protoplanets embedded in a protoplanetary disc whereby a giant protoplanet is caught up, before having migrated all the way to the central star, by a lighter outer giant protoplanet. This outer protoplanet may get captured into the 2:3 resonance with the more massive one, in which case the gaps that the two planets open in the disc overlap. Two effects arise, namely a squared mass-weighted torque imbalance and an increased mass flow through the overlapping gaps from the outer disc to the inner disc, which both play in favour of an outwards migration. Indeed, under the conditions presented here, which describe the evolution of a pair of protoplanets respectively Jupiter- and Saturn-sized, the migration is reversed, while the semimajor axis ratio of the planets is constant and the eccentricities are confined to small values by the disc material. The long-term behaviour of the system is briefly discussed, and could account for the high eccentricities observed for the extrasolar planets with semimajor axis

Endothelin-1 synthesis reduced by red wine

Abstract: Statistical evidence of reduced coronary heart disease in areas of high wine consumption has led to the widespread belief that wine affords a protective effect. Although moderate drinking of any alcohol helps to reduce the incidence of coronary heart disease, there is no clear evidence that red wine confers an additional benefit. Here we show that red wines strongly inhibit the synthesis of endothelin-1, a vasoactive peptide that is crucial in the development of coronary atherosclerosis. Our findings indicate that components specific to red wine may help to prevent coronary heart disease.

A High Spatial Resolution Analysis of the MAXIMA-1 Cosmic Microwave Background Anisotropy Data

Abstract: We extend the analysis of the MAXIMA-1 cosmic microwave background (CMB) data to smaller angular scales. MAXIMA, a bolometric balloon experiment, mapped a 124 deg$^2$ region of the sky with 10\arcmin resolution at frequencies of 150, 240 and 410 GHz during its first flight. The original analysis, which covered the multipole range $36 \leq \ell \leq 785$, is extended to $\ell = 1235$ using data from three 150 GHz photometers in the fully cross-linked central 60 deg$^2$ of the map. The main improvement over the original analysis is the use of 3\arcmin square pixels in the calculation of the map. The new analysis is consistent with the original for $\ell 785$, where inflationary models predict a third acoustic peak, the new analysis shows power with an amplitude of $56 \pm 7$ \microk at $\ell \simeq 850$ in excess to the average power of $42 \pm 3$ \microk in the range $441 < \ell < 785$.

R&D Networks

Abstract: textMany markets are characterized by a high level of inter-firm collaboration in R&D activity. This paper develops a simple model of strategic networks which captures two distinctive features of such collaboration activity: bilateral agreements and non-exclusive relationships. We study the effects of collaborations on individual R&D effort, cost reduction, and market performance. We then examine the incentives of firms to form collaborative links and the architecture of strategically stable networks. Our analysis highlights the interaction between market competition and R&D network structure. We find that if firms are Cournot competitors then individual R&D effort is declining in the level of collaborative activity. However, cost reduction and social welfare are maximized under an intermediate level of collaboration. In some cases, firms can gain market power, and even induce exit of rival firms, by forming suitable collaboration agreements. Moreover, under certain circumstances, such asymmetric collaboration networks are also strategically stable. By contrast, if firms operate in independent markets then individual R&D effort is increasing in the level of collaborative activity. Cost reduction and social welfare are maximized under the complete network, which is also strategically stable.