Shoot Meristem Function and Leaf Polarity: The Role of Class III HD–ZIP Genes

The shoot apical meristem comprises an organized cluster of cells with a central region population of self-maintaining stem cells providing peripheral region cells that are recruited to form differentiated lateral organs. Leaves, the principal lateral organ of the shoot, develop as polar structures typically with distinct dorsoventrality. Interdependent interactions between the meristem and developing leaf provide essential cues that serve both to maintain the meristem and to pattern dorsoventrality in the initiating leaf. A key component of both processes are the class III HD–ZIP genes. Current findings are defining the developmental role of members of this family and are identifying multiple mechanisms controlling expression of these genes

Sustainable energy for whom? Governing pro-poor, low-carbon pathways to development: lessons from solar PV in Kenya

Using a combination of insights from innovation studies, sociotechnical transitions theory and the STEPS pathways approach, this paper analyses the evolution of the Kenyan photovoltaics (PV) market. Considered by many to be an exemplar of private sector led development, the Kenyan PV market has witnessed the adoption of more than 300,000 solar home systems and over 100,000 solar portable lights. The notion of an entrepreneurially driven unsubsidised solar market has proved to be a powerful narrative amongst development actors who, paradoxically, have provided millions of dollars of funding to encourage the market’s development. We argue that this donor support has been critical to the success of the market, but not simply by helping to create an enabling environment in which entrepreneurs can flourish. Donor assistance has been critical in supporting a range of actors to build the elements of a PV innovation system by providing active protection for experimentation, network-building, and the construction of shared visions amongst actors throughout supply chains and amongst users.This analysis gives important clues for designing climate and development policies, with implications for the governance of energy access pathways that are inclusive of poor and marginalised groups in low income countries

Impact of parametrized nonorographic gravity wave drag on stratosphere-troposphere coupling in the northern and southern hemispheres

The impact of parametrized nonorographic gravity wave drag (NOGWD) on the stratosphere-troposphere dynamical coupling in atmospheric models is relatively unexplored. Using the European Centre for Medium-Range Weather Forecasts Integrated Forecast System, we find that changes in NOGWD strength have a substantial impact on the tropospheric eddy-driven jet (EDJ) in both hemispheres, but the sense of the impact is opposite in the two hemispheres. In the Northern Hemisphere the impact occurs via changes in the amplitude and persistence of stratospheric anomalies. In the Southern Hemisphere (SH) it occurs instead via differences in the sensitivity of the EDJ to a given stratospheric anomaly, arising from changes in the seasonal cycle leading up to the polar vortex breakdown. Increasing NOGWD eliminates the springtime phase of the SH tropospheric semiannual oscillation (SAO), resulting in a more equatorward annual-mean EDJ, and showing that the SAO cannot be explained entirely from tropospheric mechanisms

ADDING MASS TO THE SHOE DOES NOT AFFECT BALL VELOCITY IN A SOCCER PENALTY KICK

The aim of this study was to identify the optimum shoe mass that maximizes ball velocity in a soccer instep penalty kick. Two players performed 20–30 maximum-effort penalty kicks while wearing football shoes with lead weights attached to the base of the shoe (total mass: 0.26 – 0.81 kg). The kicks were recorded by a video camera at 100 Hz and a biomechanical analysis was conducted to obtain measures of ball projection velocity and kinematics of the kicking leg. We found that ball velocity was insensitive to shoe mass (at least for the range of shoe mass tested). An important contributing factor to the observed relationship was that the velocity of the kicking foot at ball impact decreased as the mass of the shoe increased. Our result indicates that players should not change their shoes before taking a penalty kick

Deterministic models of Southern Hemisphere circulation variability

Statistical models of atmospheric variability typically attempt to account for deterministic seasonal variations by constructing a long-term average for each day or month of the year. Year-to-year variability can then be treated as some form of stochastic process about this long-term average. In general, the stochastic processes are assumed to be statistically stationary (invariant under time translation). However, for a non-linear system such as the Earth’s atmosphere, multiple seasonal evolutions may be possible for the same external forcing. In the presence of such a multiplicity of solutions, the identification of a seasonal cycle with a long-term average may not be the optimal procedure. Previous research has suggested that multiple evolutions of the seasonal cycle of the Southern Hemisphere mid-latitude circulation may be possible. The central goal of this thesis is to build on this work and to present evidence for different seasonal evolutions of the Southern Hemisphere mid-latitude circulation. This evidence is initially presented by highlighting a low-frequency peak in an aspect of the Southern Hemisphere mid-latitude circulation that is viewed as a harmonic of the annual cycle (quasi-two year). Statistically stationary models of variability about a long-term average are argued to be unable to account for the presence of this harmonic. Following this, an alternative model of circulation variability is proposed that explicitly references various stages of the seasonal cycle in a deterministic manner. In particular, explicit reference is made to the downward shift and to the final breakdown of the stratospheric polar vortex. A re-interpretation of several previous results in the literature including Southern Annular Mode persistence timescales, Southern Hemisphere mid-latitude climate change and the semi-annual oscillation of the mid-latitude jet is subsequently presented using this alternative perspective

Frequency domain characteristics of ground reaction forces during walking of young and elderly females

Objective. To examine the frequency domain characteristics of the ground reaction forces of young and elderly females during free walking. Design. Independent t-tests were used to examine the frequency content of all three components of the ground reaction force. Background. Frequency domain analysis has the potential to assist in identifying changes in gait that may be masked in the time domain. No research has been done to identify changes in gait due to age-related impairments in the frequency domain. Methods. Ten young and ten elderly females walked at a prescribed speed while ground reaction forces were collected via a force platform. The highest frequency required to reconstruct the 99% of the signal’s power in each direction was calculated from the ground reaction forces. Results. The frequency content significantly decreased in the anterior–posterior direction for the young group. No significant differences were found for the other two directions (vertical and mediolateral) between the two groups. The elderly had a significantly higher frequency content compared with the young in the anterior–posterior direction. Conclusions. Ageing differences were detected using the frequency domain analysis for the anterior–posterior direction. It is possible that these differences were the result of the decrease in walking speed associated with the elderly group. Relevance Frequency domain analysis of the ground reaction forces is a useful addition to the gait analyst’s armamentarium especially when such changes are not obvious in the time domain

A study of the electrical basis for the inhibition and excitation in autonomically innervated smooth muscle

The aim of this thesis was to investigate the electrical and mechanical responses to inhibitory non-adrenergic noncholinergic (NANC) nerve stimulation in the bovine retractor penis muscle (BRP) and compare them with those to an inhibitory extract made from this muscle. The extract may contain the NANC inhibitory transmitter of the BRP and possibly of other smooth muscles. Because of species differences in the electrical response to NANC nerves in the rat and rabbit anococcygeus the effects of the extract on these tissues was also investigated. Prior to the investigation of the extract, both the excitatory and inhibitory responses to field stimulation in the BRP, and the effects of passive membrane potential displacement were studied using conventional intra- or extracellular (sucrose gap) recording techniques. The majority of cells in the BRP were electrically quiescent independent of the resting tone. The most frequent (in approximately 25% of preparations) form of spontaneous activity, oscillations in membrane potential and tone, may represent a pacemaker activity. The BRP had cable properties; the time constant and space constant indicated a high membrane resistance. In the absence of tone, field stimulation of the BRP evoked excitatory junction potentials (ejps) in every cell impaled and contractions, graded with the strength, frequency and number of pulses; spikes were not observed. Guanethidine (1-3 x 10-5M) abolished the ejps and contractions, confirming their adrenergic origin. Noradrenaline added exogenously depolarised and contracted the muscle. These effects were blocked by the a-adrenoceptor antagonists, phentolamine and prazosin. However, phentolamine (2.5x 10-6M) inhibited the contraction without reducing the ejp significantly. These effects may be independent of adrenoceptor blockade or the ejp may be mediated by a substance other than noradrenaline (e.g. ATP) released from adrenergic nerves. Prazosin (1.4 x lO-6M) failed to block either the ejp or contraction, indicating the possible existence of two types of adrenoceptor in the BRP; one activated by neuronally-released and the other by exogenously-added noradrenaline. ATP, a contaminant in the extract, also depolarised and contracted the BRP. Physostigmine reduced whilst atropine enhanced the ejps and contractions without similarly affecting the response to exogenous noradrenaline. This confirmed the presence of a cholinergic inhibitory innervation acting on the excitatory adrenergic fibres (Klinge and Sjostrand, 1977). TEA (1 x lO-4M) enhanced the ejp and contraction. Higher concentrations (0.5 to 10 x 10-3M) depolarised, increased the tone and evoked electrical and mechanical oscillations but no spikes. The depolarisation and contraction to exogenous noradrenaline were not enhanced, indicating that TEA acts on the adrenergic nerves. Some post-synaptic effect to block K+ channels also seems likely. The relationship between ejp amplitude and membrane potential in the double sucrose gap was linear and indicated a reversal potential more positive than -30mV. Electrotonic pulse amplitude decreased during the ejp, indicating an increased membrane conductance. Ejps and contractions were reduced following the replacement of the NaCl of the Krebs solution with sodium glutamate. This may be due to the effects of glutamate itself (e.g. Ca2+ chelation) rather than reduction in the membrane Cl- gradient. Tone usually developed spontaneously and was accompanied by membrane depolarisation (from -53 to -45mV) which may open voltage-dependent channels, causing Ca2+ entry and/or its release from intracellular binding sites. Field stimulation produced inhibitory potentials (ijps) and relaxations graded with the strength and number of pulses but showing little frequency dependence. Rebound depolarisation and contraction often followed the ijp and relaxation. Tetrodotoxin (3 x IO-6M), but not adrenergic or cholinergic antagonists, abolished the ijp and relaxation, confirming their non-adrenergic non-cholinergic neurogenic nature. The extract, prepared and acid-activated as described by Gillespie, Hunter and Martin (1981), hyperpolarised and relaxed the BRP, as did sodium nitroprusside and adenosine triphosphate (ATP). Unlike the activated extract or sodium nitroprusside, desensitisation to ATP occurred rapidly and without any change in the inhibitory electrical or mechanical responses to field stimulation. The ijp and relaxation in the BRP were insensitive to apamin but abolished by oxyhaemoglobin (4-8 x 10-6M), as were the responses to extract and sodium nitroprusside. In TEA (10-2M), field stimulation evoked relaxations with no accompanying electrical change. The ijp may be unconnected with or additional to another mechanism producing relaxation. The relationship between membrane potential and ijp in the BRP was non-linear. Ijp amplitude was initially increased during membrane potential displacement from -45mV to approximately -60mV. Thereafter (-60 to -l03mV) the ijp was reduced. Ijps were abolished at -27 and -103mV; reversal was not observed. The hyperpolarisation to extract was also enhanced during passive displacement of the membrane potential to more negative values (-57mV). Membrane resistance increased during the ijp. The extract produced inconsistent changes in membrane resistance, possibly because of the presence of more than one active component. K+ withdrawal failed to enhance the ijp or hyperpolarisation to extract and 20mM K+ did not abolish the the ijp at membrane potentials exceeding EK (-49mV). Thus, the ijp or hyperpolarisation to extract are unlikely to be mediated by an increased K+ conductance. Reducing the Cl- abolished the hyperpolarisation to field stimulation and extract. This occurred more quickly than the anticipated reduction in the Cl- gradient and may be due to Ca2+ chelation by the anion substitute (glutamate or benzenesulphonate) or blockade of the resting conductance which is normally inactivated by the transmitter. Ouabain (1-5x 10-5M), which reduces both the Na+ and Cl- gradients, abolished the ijp, implicating either of these ions as the ionic species involved. In the rat and rabbit anococcygeus, field stimulation and extract each reduced guanethidine-induced tone. This was unaccompanied in the majority of cells in the rat by any significant electrical response. In the remaining cells, inhibition of the membrane potential oscillations occurred. The rabbit anococcygeus differed in that inhibition of the electrical oscillations was observed in every cell exhibiting this behaviour. However, the majority of cells in the rabbit were electrically quiescent and showed only small hyperpolarisations to field stimulation and no electrical response to extract. Apamin (1 x 10-7M) failed to block the electrical and mechanical response to field stimulation in the rabbit but did inhibit transiently that to extract. The latter effect may be due to the initial excitatory effects of apamin. The similarities between the electrical effects of the extract and those of inhibitory nerve stimulation in the BRP, rat and rabbit anococcygeus muscles are generally consistent with their being mediated by the same active component. Moreover, the ijp in the BRP shows properties which have not been reported in other non-adrenergic noncholinergically innervated smooth muscles

Non-stationarity in Southern Hemisphere climate variability associated with the seasonal breakdown of the stratospheric polar vortex

Statistical models of climate generally regard climate variability as anomalies about a climatological seasonal cycle, which are treated as a stationary stochastic process plus a long-term seasonally dependent trend. However, the climate system has deterministic aspects apart from the climatological seasonal cycle and long-term trends, and the assumption of stationary statistics is only an approximation. The variability of the Southern Hemisphere zonal-mean circulation in the period encompassing late spring and summer is an important climate phenomenon and has been the subject of numerous studies. It is shown here, using re-analysis data, that this variability is rendered highly non-stationary by the organizing influence of the seasonal breakdown of the stratospheric polar vortex, which breaks time symmetry. It is argued that the zonal-mean tropospheric circulation variability during this period is best viewed as interannual variability in the transition between the springtime and summertime regimes induced by variability in the vortex breakdown. In particular, the apparent long-term poleward jet shift during the early-summer season can be more simply understood as a delay in the equatorward shift associated with this regime transition. The implications of such a perspective for various open questions are discussed