Oxidation of biogenic and water-soluble compounds in aqueous and organic aerosol droplets by ozone: a kinetic and product analysis approach using laser Raman tweezers

The results of an experimental study into the oxidative degradation of proxies for atmospheric aerosol are presented. We demonstrate that the laser Raman tweezers method can be used successfully to obtain uptake coeffcients for gaseous oxidants on individual aqueous and organic droplets, whilst the size and composition of the droplets is simultaneously followed. A laser tweezers system was used to trap individual droplets containing an unsaturated organic compound in either an aqueous or organic ( alkane) solvent. The droplet was exposed to gas- phase ozone and the reaction kinetics and products followed using Raman spectroscopy. The reactions of three different organic compounds with ozone were studied: fumarate anions, benzoate anions and alpha pinene. The fumarate and benzoate anions in aqueous solution were used to represent components of humic- like substances, HULIS; a alpha- pinene in an alkane solvent was studied as a proxy for biogenic aerosol. The kinetic analysis shows that for these systems the diffusive transport and mass accommodation of ozone is relatively fast, and that liquid- phase di. ffusion and reaction are the rate determining steps. Uptake coe. ffcients, g, were found to be ( 1.1 +/- 0.7) x 10(-5), ( 1.5 +/- 0.7) x 10 (-5) and ( 3.0 - 7.5) x 10 (-3) for the reactions of ozone with the fumarate, benzoate and a- pinene containing droplets, respectively. Liquid- phase bimolecular rate coe. cients for reactions of dissolved ozone molecules with fumarate, benzoate and a- pinene were also obtained: k(fumarate) = ( 2.7 +/- 2) x 10 (5), k(benzoate) = ( 3.5 +/- 3) x 10 (5) and k(alpha-pinene) = ( 1-3) x 10(7) dm(3) mol (-1) s (- 1). The droplet size was found to remain stable over the course of the oxidation process for the HULIS- proxies and for the oxidation of a- pinene in pentadecane. The study of the alpha- pinene/ ozone system is the first using organic seed particles to show that the hygroscopicity of the particle does not increase dramatically over the course of the oxidation. No products were detected by Raman spectroscopy for the reaction of benzoate ions with ozone. One product peak, consistent with aqueous carbonate anions, was observed when following the oxidation of fumarate ions by ozone. Product peaks observed in the reaction of ozone with alpha- pinene suggest the formation of new species containing carbonyl groups

Reconstruction of the trachea with a tubed radial forearm free flap

AbstractBackgroundWe present the case of a patient with adenoid cystic carcinoma of the trachea who had 60 mm of the trachea excised and reconstructed with a stented radial forearm free flap. The patient was well in the immediate postoperative period with good function of the neotrachea. Problems developing after the reconstruction included proximal stricture, sputum retention, and recurrent pneumonia.ResultThe patient died of malignant hypercalcemia 16 months after the reconstruction. To our knowledge this is the first reported case of a total tracheal resection and reconstruction with a combination of free tissue transfer and internal stenting.ConclusionWe conclude that tracheal reconstruction has the potential to provide a reliable airway in patients not able to be reconstructed with a primary anastomosis

Experimental constraints on the parameter space of the next-to-minimal supersymmetric standard model at LEP 2

We search for the neutral Higgs sector of the next-to-minimal supersymmetric standard model at LEP 2. At the tree level any experimental constraints on $\tan \beta$ cannot be set by the Higgs search at LEP 2 with $\sqrt{s}$ = 175 GeV, whereas at LEP 2 with $\sqrt{s}$ = 192 GeV $\tan \beta$ can be set by an experimental constraint. Furthermore the tree level parameter space of the model can be completely explored by the Higgs search at LEP 2 with $\sqrt{s}$ = 205 GeV. Radiative corrections both to the neutral Higgs boson masses and to the relevant couplings for the scalar Higgs productions give large contributions to the production cross sections of the scalar Higgs bosons at the tree level. The tree level situation at LEP 2 with $\sqrt{s}$ = 192 GeV as well as with $\sqrt{s}$ = 205 GeV can be drastically changed by these effects. We expect that a small region of the 1-loop level parameter space of the model via the scalar Higgs production can be explored by the Higgs search at LEP 2.Comment: 14 pages (3 figures are included

Expedition 302 summary

The first scientific drilling expedition to the central Arctic Ocean was completed in September 2004. Integrated Ocean Drilling Program Expedition 302, Arctic Coring Expedition (ACEX), recovered sediment cores to 428 meters below seafloor (mbsf) in water depths of ~1300 m, 250 km from the North Pole.Expedition 302's destination was the Lomonosov Ridge, hypothesized to be a sliver of continental crust that broke away from the Eurasian plate at ~56 Ma. As the ridge moved northward and subsided, marine sedimentation occurred and continues to the present, resulting in what was anticipated from seismic data to be a continuous paleoceanographic record. The elevation of the ridge above the surrounding abyssal plains (~3 km) ensured that sediments atop the ridge were free of turbidites. The primary scientific objective of Expedition 302 was to continuously recover this sediment record and to sample the underlying sedimentary bedrock by drilling and coring from a stationary drillship.The biggest challenge during Expedition 302 was maintaining the drillship's location while drilling and coring in 2–4 m thick sea ice that moved at speeds approaching 0.5 kt. Sea-ice cover over the Lomonosov Ridge moves with one of the two major Arctic sea-ice circulation systems, the Transpolar Drift, and responds locally to wind, tides, and currents. Until now, the high Arctic Ocean Basin, known as "mare incognitum" within the scientific community, had never before been deeply cored because of these challenging sea-ice conditions.Initial results reveal that biogenic carbonate is present only in the Holocene–Pleistocene interval. The upper 198 mbsf represents a relatively high sedimentation rate record of the past 18 m.y. and is composed of sediment with ice-rafted debris and dropstones, suggesting that ice-covered conditions extended at least this far back in time. Details of the ice type (e.g., iceberg versus sea ice), timing, and characteristics (e.g., perennial versus seasonal) await further study. A hiatus occurs at 193.13 mbsf, spanning a 25 m.y. interval from the early Miocene to the middle Eocene between ~18 Ma and 43 Ma. The sediment record during the middle Eocene is of dark, organic-rich biosiliceous composition. Isolated pebbles, interpreted as ice-rafted dropstones, are present down to 239 mbsf, well into this middle Eocene interval. Around the lower/middle Eocene boundary an abundance of Azolla spp. occurs, suggesting that a fresh and/or low-salinity surface water setting dominated the region during this time period. Although predrilling predictions based on geophysical data had placed the base of the sediment column at 50 Ma, drilling revealed that the uppermost Paleocene to lowermost Eocene boundary interval, well known as the Paleocene/Eocene Thermal Maximum (PETM), was recovered. During the PETM, the temperature of the Arctic Ocean surface waters exceeded 20°C.Drilling during Expedition 302 also penetrated into the underlying sedimentary bedrock, revealing a shallow-water depositional environment of Late Cretaceous age

Methods

Information assembled in this chapter will help the reader understand the basis for the preliminary conclusions of the Expedition 302 Scientists and will also enable the interested investigator to select samples for further analyses. This information concerns offshore and onshore operations and analyses described in the "Sites M0001–M0004" chapter. Methods used by various investigators for shore-based analyses of Expedition 302 samples will be described in the individual contributions published in the Expedition Research Results and in various professional journals

Sites M0001–M0004

Operations Mobilization of Vidar Viking, Aberdeen, ScotlandThe Vidar Viking came under contract on 22 July 2004, when mobilization began in Aberdeen, Scotland. Mobilization in Aberdeen included two major installations: a moonpool and a full coring/drilling spread. By 26 July, all equipment for the Vidar Viking had arrived, including information technology equipment bound for the Oden. The derrick was load-tested and certified. The Vidar Viking took on a full complement of fuel at Aberdeen.Test Coring Site: Witch Ground, North SeaThe Vidar Viking set sail for Landskrona, Sweden, on 28 July 2004. While the ship was en route, a first test of the drilling equipment was conducted in the Witch Ground area of the North Sea, ~8 h steam from Aberdeen. A test borehole was drilled in 152 m water depth to a depth of 37 meters below seafloor (mbsf) using the British Geological Survey's (BGS's) advanced piston corer (APC) and extended core barrel. Cores were obtained with both systems. The APC recovered >4 m in all runs (maximum = 4.5 m). The Vidar Viking left the test coring site at 1900 h on 30 July and proceeded to Landskrona.Meanwhile, mobilization of the Oden proceeded at Gothenburg, Sweden, which included loading the laboratory equipment. On the evening of 31 July, the Oden set sail for Tromsø, Norway.Mobilization of Vidar Viking, Landskrona, SwedenThe Vidar Viking reached Landskrona on the morning of 1 August 2004. The stern notch, a 100 ton section required by the Vidar Viking when working in ice, and the helideck were installed. The remaining containers were loaded onto the deck, including the core and European Consortium for Ocean Research Drilling Science Operator curation containers sent from Bremen, Germany. Other mobilization work continued until the morning of 3 August, when the Vidar Viking departed for Tromsø.Mobilization of Vidar Viking and Oden, Tromsø, NorwayThe Oden arrived in Tromsø on the evening of 5 August 2004. The Vidar Viking arrived on the morning of 7 August. Two helicopters, required for ice reconnaissance missions, landed on the Oden and were secured.Rendezvous of three Expedition 302 shipsExpedition 302 officially began when the Oden left Tromsø, Norway, at 2350 h on 7 August 2004. The Vidar Viking remained in Tromsø for the next 12 h to wait for dynamic positioning spare parts to arrive.The Oden transited to 81°56'N, 44°59'E to meet the other two ships in the Arctic Coring Expedition (ACEX) fleet for Expedition 302, the Sovetskiy Soyuz and the Vidar Viking, at the edge of the polar ice pack on 10 August. The fleet entered the ice together with the Sovetskiy Soyuz leading, the Oden following, and the Vidar Viking bringing up the rear.Transit to first siteDuring the transit to the operational area, ice reconnaissance and personnel transfer flights began on 12 August 2004. The fleet made unprecedented headway of 8–10 kt in sea ice.The fleet arrived on site at 2350 h on 13 August and began preparations for drilling and operations for maintaining position in sea ice.Preparations for drilling began with clearing ice from the moonpool. Once this was done, a steel skirt was deployed through and below the moonpool to protect the drill string from ice impact below the hull. Once the ice protection skirt was in place, the drill floor and iron roughneck were installed. The drill floor was ready for operations by 0900 h on 15 August.During this time, the fleet's ability to maintain station was tested by positioning the Sovetskiy Soyuz and the Oden upstream of the Vidar Viking. The initial stationkeeping tests were successful, and the Fleet Manager gave approval to start drilling operations at 1100 h on 15 August.Site operationsCores were recovered in five holes (Holes M0002A, M0003A, M0004A, M0004B, and M0004C) (Table T1). Hole M0001A was abandoned after the bottom-hole assembly (BHA) was lost. Logging was attempted in two holes and data were collected in Hole M0004B.Table T2 documents the allocation of time, broken down into (1) waiting for better ice conditions, (2) operational breakdown, and (3) drilling operations.Waiting for better ice conditions was labeled "W." If waiting on ice conditions required pulling pipe and subsequent preparations to begin drilling operations, these times were included in the W category because that time delay was caused by the "waiting for ice" situation. "Breakdown time" is defined as operational time consumed as a result of equipment or mechanical failure. The loss of a BHA, for example, regardless if caused by human error or mechanical failure, necessitated a drill string trip. If the trip time was caused by equipment failure, it was considered as breakdown time "B."Site M0001 (SP 2720 on Line AWI 91090)Site M0001 (shotpoint [SP] 2720 on Line AWI 91090) was reached at 1100 h on 15 August 2004. Later that day during drill string deployment, the high-pressure mud valve on the top drive was damaged. The valve was removed, the rest of the drill string was run, and then the broken valve was replaced. Pipe trips were slowed or stopped intermittently to allow overheated hydraulic fluid in the new drill rig to cool.By 16 August, the drill string was deployed to the seafloor and the first piston corer was deployed at 0600 h. After pumping for 30 min, pressure was not obtained and the piston corer was retrieved without having fired. Damaged seals on the piston corer were replaced. Ice conditions were marginal, and at 0900 h operations were stopped and the drill string was lifted from the seabed. Ice conditions improved by 1400 h, and operations continued. The piston corer was deployed again, and no pressure developed in the drill string. Upon retrieval, the piston corer had not fired. It was suspected that the piston corer had not latched into the BHA. The extended core barrel was then deployed but was not recovered, which indicated that the BHA was lost. At 2000 h, the drill string was tripped to the surface and the BHA and extended core barrel losses were confirmed.Beginning early on 17 August, a new BHA was assembled and lowering of the drill string began. When >800 m was deployed, the high-pressure mud valve on the swivel was damaged during pipe handling. The drill string was tripped to the surface because the operator did not want to risk leaving the drill string hanging in the water column for an unspecified period of time. After completing the pipe trip, the damage was assessed and the Oden's chief engineer was tasked with manufacturing a new valve using materials from a spare pup joint. As an interim solution, a conventional valve assembly was installed, which restricted operations so that no piston core could be deployed.Ice conditions deteriorated between 0900 and 2200 h, and the time was utilized to move the Vidar Viking to a new position (Hole M0002A). Because there were no mud valve spares, the Swedish Polar Research Secretariat began making arrangements for a Swedish Air Force C-130 airdrop of two new valve parts and one conventional valve assembly.Site M0002 (SP 2560 on Line AWI-91090)Based on a strategy developed by the ice management team, the drill string was lowered while drifting onto the location of Site M0002. By 2200 h on 18 August 2004, this strategy put the Vidar Viking within 190 m of the proposed site. The final positioning was done by icebreaking this short distance to Hole M0002A. Once on location at 0820 h, three more drill pipes were added and coring started. Because the mud valve was not yet repaired, the extended core barrel was deployed instead of the APC. A first attempt at coring was unsuccessful, but after adding more pipe and drilling another core run, some core was retrieved. The first core on deck arrived at 1335 h at a water depth of 1209 m. Drilling operations continued throughout the afternoon. The newly fabricated mud valve from the Oden arrived late in the afternoon, and preparations were made for its installation during a wireline trip. The temporary valve was replaced before more drill pipe was added for the next core run. By midnight on 19 August, a depth of 31 mbsf had been reached.Drilling and extended core barrel coring continued until 23 August (Table T1) when the Fleet Manager ordered the drill pipe to be pulled to 40 mbsf because ice conditions had deteriorated. Permission to continue drilling operations was given midday, and operations continued until 2100 h when the ice conditions forced the termination of Hole M0002A at a depth of 271.69 m.The drill string was tripped to the drill deck during the morning of 24 August. After waiting for ice conditions to change in the afternoon, a transit began at 1930 h to a position from which the Vidar Viking could drift onto location while tripping in the drill string.While we waited for improved ice conditions and operations set up for the next site continued, an air gun seismic survey was run from the Oden to tie Site M0002 to the next site (Site M0003).Site M0003 (SP 2521 on Line AWI-91090)The Vidar Viking reached the ice-drift position at 2100 h and awaited ice reconnaissance results. The iron roughneck, which had been removed to repair oil leaks, was installed after repairs; the ice protector skirt was lowered; and the drill floor was prepared. At 2300 h, the BHA and drill collars were run. At 0240 h on 25 August 2004, after 400 m of pipe had been deployed, the housing of the iron roughneck cracked and had to be removed for major repairs. Operations resumed at 1400 h using power tongs. The seafloor was reached at ~2300 h, and at 0110 h on 26 August, the first APC core was recovered from Hole M0003A (Table T1).A second APC core with a shattered liner was recovered. The third APC core became stuck in the BHA. While trying to release the corer, the wireline parted at the mechanical termination, and it was necessary to pull the string. Hole M0003A was terminated at 0440 h.The ice management team conducted ice reconnaissance surveys, reviewed options, and recommended that the fleet move to a location farther west, where a longer-term prediction of relatively good ice could be made. Once the site was selected, the ice team predicted an upstream ice position for the Vidar Viking to start to drift onto the new location. The fleet steamed to the updrift ice position, arriving at 0630 h on 27 August. During this time, wireline termination repair, APC service, and iron roughneck testing and refitting took place.Site M0004 (SP 3006 [Holes M0004A and M0004B] and 3004 [Hole M0004C] on Line AWI-91090)At 0755 h on 27 August 2004 during the pipe trip to the seafloor, the high-pressure mud valve was damaged again. The valve was removed, and the remaining string was run to 1150 m depth while the valve was repaired. At 1800 h, the Vidar Viking was on location (Hole M0004A). Once on station, the repaired mud valve was installed and the drill string was run to the seabed. At 2230 h, drilling operations in Hole M0004A commenced and the hole was advanced by washing ahead to 17 mbsf (Table T1) before a piston corer was deployed.Shortly after midnight on 28 August 2004, the APC became stuck in the BHA but was freed after ~1 h. Once on deck, the plastic liner in the core barrel was found to be shattered and 3.5 m of the core was stuck in the barrel. In light of these problems with the APC—in particular, the risk of junking the hole again—it was decided to switch to extended core barrel coring. Two extended core barrel cores were recovered to a depth of 30.5 mbsf followed by washing to 265 mbsf using the insert bit. This decision to wash ahead was made in order to recover sediment deeper than that recovered in Hole M0002A. By 2240 h, a depth of 265 mbsf was reached.Extended core barrel coring operations continued for the next 3 days (29–31 August), where the hole was advanced at varying rates with good to poor recovery. During this time, the drilling was very slow (e.g., 1 m/h) and recovery in many cores was zero (Cores 302-M0004A-13X through 18X). Different strategies were tried to improve the advance rate. At times, the hole was advanced by washing ahead in an attempt to make faster progress but this strategy was ultimately abandoned after it was found that the washing rate was almost the same as the coring rate. On 31 August from 0200 to 0500 h, for two coring runs in a row no core was recovered. The extended core barrel shoe was switched to a coring shoe for a third attempt at recovery. This coring run cleared a blockage in the bit as evidenced by a large drop in pump pressure. Following this core (with good recovery) and after clearing the blocked bit, core recovery and advancement improved over the next 12 h until basement was reached in Core 302-M0004A-35X. Basement penetration was difficult (8 m penetration in 12 h with low core recovery), and a decision was made at 0900 on 1 September to stop coring at a total depth of 428 mbsf and conduct logging in Hole M0004A.The logging tools were moved to the rig floor, and the tool string (Formation MicroScanner–Accelerator Porosity Sonde–Natural Gamma Ray Spectroscopy Tool–Scintillation Gamma Ray Tool [FMS-APS-NGT-SGT]) and wireline rig-up proceeded simultaneously. The run into hole commenced at 2130 h. This was done at low speed in order to allow the tools to warm up. Communication with the tool was initially established, and it was lowered to the end of the drill pipe. A computer malfunction caused a communication loss to the tools. The problem was corrected by 0200 h. The tool was powered up, and attempts were made to get the tool to pass through the BHA into the open hole. All efforts failed at the same depth (~1366 meters below rig floor [mbrf]); so, while at rest at this depth, the calipers were opened on the FMS to check whether it was free or lodged. The calipers had some movement, which indicated that the tool string was free.The landing ring for the core barrel is the narrowest section of the whole pipe string (95 mm) and lies ~6 m above the bit. All the logging tools had been checked through a landing ring dockside in Aberdeen, but there was no hole calibration ring on board that could be used as a second check. Sequentially, four more logging attempts were made. Each time, it was assumed that the logging tools were too large in diameter and the string diameter was further reduced by removing the larger diameter components. The APS bowspring was removed first, followed by the knuckle joint. Finally, only the narrowest velocity-density string was deployed, which failed to clear the bit at the same depth as the previous runs. After the fifth attempt failed, the logging time allocated had been consumed and attempts to log Hole M0004A ended at 1045 h on 2 September.After the logging gear was cleared away and the drill string was lifted out of the seabed, preparations were made to start a second hole (Hole M0004B) at the site. During preparations, the inner barrel was deployed but did not latch. After an improvised downhole hammer was deployed and worked for 2 h, a short length of core (~10 cm of mudstone), which had been partially blocking the BHA, was recovered.By 2030 h on 2 September, the Vidar Viking was at the new position for the next hole (Hole M0004B). Coring in Hole M0004B started at a depth of 10 mbsf using the extended core barrel because the APC was deemed too risky. After retrieving the first sample, the hole was washed to 20 mbsf for an in situ temperature measurement. The BGS temperature probe was lowered to the base of the hole, pushed into the sediment, and programmed to record the temperature every 5 s. The probe was left to record temperature for 40 min, after which it was retrieved. Plans to wash to a depth of 215 mbsf, core to 230 mbsf, and then wash to 250 mbsf and log were stymied by problems with drilling pressure lines/gauges freezing at –10?C. Because of these problems and the limited time left, the hole was only advanced to a depth of 220 mbsf. Temperature measurements were made at 60 and 100 mbsf.At 0000 h on 4 September, the pipe was pulled to 65 mbsf to prepare for logging. Rigging of the wireline and tool string occurred concurrently, and rig-up of both was completed by 0415 h. The tool string comprised the FMS-Borehole Compensated Sonic (BHC)-NGT-SGT; the choice of tools was such that it coul

Sedimentation record in the Konkan-Kerala Basin: implications for the evolution of the Western Ghats and the Western Indian passive margin

The Konkan and Kerala Basins constitute a major depocentre for sediment from the onshore hinterland of Western India and as such provide a valuable record of the timing and magnitude of Cenozoic denudation along the continental margin. This paper presents an analysis of sedimentation in the Konkan-Kerala Basin, coupledwith a mass balance study, and numerical modelling of flexural responses to onshore denudational unloading and o¡shore sediment loading in order to test competing conceptual models for the development of high-elevation passive margins. The Konkan-Kerala Basin contains an estimated 109,000 km<sup>3</sup>; of Cenozoic clastic sediment, a volume difficult to reconcile with the denudation of a downwarped rift flank onshore, and more consistent with denudation of an elevated rift flank. We infer from modelling of the isostatic response of the lithosphere to sediment loading offshore and denudation onshore that flexure is an important component in the development of the Western Indian Margin.There is evidence for two major pulses in sedimentation: an early phase in the Palaeocene, and a second beginning in the Pliocene. The Palaeocene increase in sedimentation can be interpreted in terms of a denudational response to the rifting between India and the Seychelles, whereas the mechanism responsible for the Pliocene pulse is more enigmatic

Red lists for cultivated species: why we need it and suggestions for the way forward

The world's food basket is today shrinking at an alarming rate and most concerning is the reduction in the number of species and varieties used by humankind for food and nutrition, which raises serious concerns about the sustainability of feeding the world today and in the future. Yet, whereas we deploy consistent efforts in monitoring the status of wild biodiversity, very limited is the research in monitoring diversity of plants used by farmers, assess threats of genetic erosion, understand how diversity is helping farmers in coping with climate change, etc. Documenting and monitoring agrobiodiversity on farm is fundamental for enhancing its sustainable use and prevent losses of both genetic diversity and indigenous knowledge to happen before it is too late. This poster explains why a Red List for Cultivated Species is needed and a proposed approach to creating one

Implications of a Massless Neutralino for Neutrino Physics

We consider the phenomenological implications of a soft SUSY breaking term BN at the TeV scale (here B is the U(1)_Y gaugino and N is the right-handed neutrino field). In models with a massless (or nearly massless) neutralino, such a term will give rise through the see-saw mechanism to new contributions to the mass matrix of the light neutrinos. We treat the massless neutralino as an (almost) sterile neutrino and find that its mass depends on the square of the soft SUSY breaking scale, with interesting consequences for neutrino physics. We also show that, although it requires fine-tuning, a massless neutralino in the MSSM or NMSSM is not experimentally excluded. The implications of this scenario for neutrino physics are discussed.Comment: 14 pages, latex, no figure

Higgs Scalars in the Minimal Non-minimal Supersymmetric Standard Model

We consider the simplest and most economic version among the proposed non-minimal supersymmetric models, in which the $\mu$-parameter is promoted to a singlet superfield, whose all self-couplings are absent from the renormalizable superpotential. Such a particularly simple form of the renormalizable superpotential may be enforced by discrete $R$-symmetries which are extended to the gravity-induced non-renormalizable operators as well. We show explicitly that within the supergravity-mediated supersymmetry-breaking scenario, the potentially dangerous divergent tadpoles associated with the presence of the gauge singlet first appear at loop levels higher than 5 and therefore do not destabilize the gauge hierarchy. The model provides a natural explanation for the origin of the $\mu$-term, without suffering from the visible axion or the cosmological domain-wall problem. Focusing on the Higgs sector of this minimal non-minimal supersymmetric standard model, we calculate its effective Higgs potential by integrating out the dominant quantum effects due to stop squarks. We then discuss the phenomenological implications of the Higgs scalars predicted by the theory for the present and future high-energy colliders. In particular, we find that our new minimal non-minimal supersymmetric model can naturally accommodate a relatively light charged Higgs boson, with a mass close to the present experimental lower bound.Comment: 63 pages (12 figures), extended versio