Histoire postglaciaire de la végétation au lac du Diable, mont Albert, Gaspésie, Québec

Au lac du Diable (494 m d'altitude), sur le flanc oriental du mont Albert (sommet: 1154 m), la colonisation végétale postglaciaire débuta par un stade ayant pu durer quelques siècles, à physionomie comparable à celle de la toundra, caractérisé d'abord par les herbes puis par les arbustes. Les populations arborescentes s'installèrent à partir de 10 600 ans BP environ. L'aire occupée par la toundra dans la région devait alors déjà se confiner, comme de nos jours, au seul sommet du mont Albert. Les peupliers et les épinettes (surtout l'épinette blanche) immigrèrent les premiers, mais le bouleau blanc était présent dès 10 300 ans BP. Autour de 10 000 ans BP, les forêts environnantes étaient déjà dominées par les épinettes, mais vers 9500 ans BP leur nombre a fortement diminué alors qu'augmentaient les populations de mélèzes, de bouleaux blancs et surtout d'aulnes verts, et ce, jusque vers 7000 ans BP; pendant ce temps, le sapin croissait dans le secteur, mais sans abonder. Cette longue régression des épinettes fut probablement provoquée par un climat plus sec ou orageux qui favorisa une grande fréquence des feux de forêts, ce qui corrobore le modèle de Milankovitch pour le climat de l'Holocène inférieur. Après 7000 ans BP, sous un climat plus humide, les populations de sapins ont alors pu se développer sur les versants, et des communautés forestières fermées associées aux sapinières-pessières y ont dominé jusqu'à nos jours. Durant la période hypsithermique (7000 à 5000-4500 ans BP environ), à part une plus grande abondance du bouleau blanc, le paysage végétal autour du lac du Diable n'a pas été modifié par l'immigration d'arbres plus thermophiles comme le bouleau jaune ou le pin blanc. Durant l'Holocène supérieur, les populations de sapins et d'épinettes eurent tendance à augmenter et celles de bouleaux blancs ont régressé, phénomène attribué au refroidissement post-hypsithermique.The postglacial plant colonization at the Lac du Diable (alt.: 494 m), on the eastern flank of Mont Albert (summit: 1154 m), started with a tundra-like phase that lasted for some centuries, and was characterized by abundant herbs, then by shrubs. Tree populations established themselves by 10 600 years BP approximately. The area of the regional landscape occupied by tundra at that time was probably restricted to the Mont Albert summit plateau, as it is nowadays. Poplars and spruces (mainly white spruce) were the first immigrants, but white birch was present as early as 10 300 BP. Around 10 000 BP, the forests surrounding Lac du Diable were dominated by spruce. However, around 9500 years BP, their abundance was greatly reduced, whereas the number of larch, white birch and especially green alder increased until 7000 BP. In the meantime, balsam fir grew in the area but was not abundant. The long-lasting decline in spruce populations was probably caused by a dry and/or stormy summer climate that favoured frequent wildfires, these conditions corroborating the Milankovitch model for the Early Holocene climate. After 7000 BP, the balsam fir populations developed under a more humid climate and closed sprucefir forests dominated the landscape around the lake until the present. During the Hypsithermal (ca. 7000 to 5000-4500 years BP), apart from a greater abundance of white birch, the vegetational landscape around Lac du Diable remained stable, without any new species like yellow birch or white pine, for instance. During the Late Holocene, there was a tendency for population increases in spruce and balsam fir, and for a decrease in white birch, a feature linked with the post-hypsithermal cooling.Am Lac du Diable (454 m Hôhe) auf der Ostseite des Mont Albert (Spitze: 1154 m) begann die postglaziale Pflanzenansiedlung mit einer Phase, die einige Jahrhunderte gedauert haben kann und die eine der Tundra vergleichbare Physiognomik hatte, zunâchst durch Grâser, dann durch Bùsche gepràgt. Die baumartigen Bestànde siedelten sich ab ungefàhr 10 600 Jahren v.u.Z. an. Der in der Gegend von der Tundra eingenommene Platz musste damais schon wie heute allein auf den Gipfel des mont Albert begrenzt sein. Die Pappeln und Fichten (vor allem Weisstannen) siedelten sich als erste an, aber die Weissbirke war seit 10 300 Jahren v.u.Z. anzufinden. Um 10 000 Jahre v.u.Z. dominierten in den umgebenden Wâldern schon die Fichten, aber gegen 9500 Jahre v.u.Z. nahm ihre Zahl stark ab, wàhrend gleichzeitig die Bestànde von Lârchen, Weissbirken und vor allem grùnen Erlen zunahmen und das bis um 7000 Jahre v.u.Z.: wàhrend dieser Zeit nahmen Tannen in dem Gebiet zu, ohne sehr zahlreich zu sein. Dieser langsame Rùckgang der Fichten wurde môglicherweise durch ein trockeneres oder durch Gewitter gepràgtes Klima hervorgerufen, welches hâufige WaIdbrànde begùnstigte, was wiederum das Modell von Milankovitch fur das Klima im frùhen Holozàn erhàrtet. Nach 7000 Jahren v.u.Z. haben die Tannenansiedlungen sich unter einem feuchteren Klima auf den Abhàngen entwickeln kônnen, und geschlossene Waldeinheiten, die mit den Fichter-Tannenwâldern in Verbindung gebracht werden, haben bis heute dort dominiert. Wàhrend des Hypsithermal (etwa 700 bis 5000-4500 Jahre v.u.Z.) wurde die Pflanzenlandschaft um den lac du Diable abgesehen von einem vermehrten Vorkommen der Weissbirke nicht durch Ansiedlung von mehr thermophilen Bàumen wie die Gelbbirke oder die Weisskierfer verândert. Wàhrend des spàten Holozân hatten die Bestànde von Tannen und Fichten die Tendenz zuzunehmen, wàhrend die der Weissbirke zurùckgingen, ein Phânomen, das der post-hypsithermischen Abkuhlung zugeschrieben wird

Histoire Postglaciaire de la Végétation dans la Région de Mont-Saint-Pierre, Gaspésie, Québec

Les analyses pollinique et macrofossile de sédiments de deux lacs des environs de Mont-Saint-Pierre (Gaspésie), l'un dans la vallée côtière, l'autre sur le plateau, permettent de reconstituer l'histoire postglaciaire de la végétation dans deux situations physiographiques contrastées. Seul le plateau a été colonisé par une végétation initiale de type toundra (> 10 400 ans BP), pendant que la vallée était encore en partie ennoyée par la mer de Goldthwait. L'afforestation du plateau fut caractérisée d'abord par des populations de Picea sp., accompagné de Populus sp. et Larix laricina, puis par un envahissement progressif par Abies balsamea et Betula papyrifera. La baisse de la représentation pollinique de l'aulne vert (Alnus cf. crispa), maximale durant l'afforestation, paraît être un indicateur assez fidèle de la fermeture de la couverture forestière. Cette phase se termine vers 9000 ans BP sur le plateau. Le rythme de l'afforestation a été différent dans la vallée. Des taxons héliophiles s'y sont maintenus plus longtemps, ce qui peut être relié à l'activité des versants abrupts qui flanquent la vallée. Malgré des variations de l'abondance relative des arbres, la sapinière à bouleau blanc a sans doute occupé le plateau depuis 9000 ans BP environ. Par contre, la végétation de la vallée s'est passablement modifiée jusque vers 5000 à 4500 ans BP, par la migration successive de Betula alleghaniensis, de Pinus strobus, de Fraxinus nigra, dAcer saccharum et d'Ulmus americana. L'implantation progressive de ces arbres relativement thermophiles est à l'origine de la diversité du paysage actuel de la vallée. Ces reconstitutions permettent d'écarter l'hypothèse de Dansereau (1944) selon laquelle les érablières à Acer saccharum de la Gaspésie seraient des groupements hérités de l'optimum climatique de l'Holocène moyen, au cours duquel les érablières auraient été largement répandues sur le territoire. Les données montrent que ces érablières datent de l'Holocène Supérieur, la migration d'Acer saccharum ayant sans doute été freinée par des barrières topo-climatiques entraînant une discontinuité prononcée des habitats pouvant accueillir cette espèce.Pollen and macrofossil diagrams from the sediments of two lakes in the Mont-Saint-Pierre area (Gaspé, Québec) allow the reconstruction of the postglacial vegetational history on the plateau and in the coastal valley nearby. Tundra prevailed on the plateau until 10,400 years BP while the valley was partly submerged by the Goldthwait Sea. The afforestation began with the invasion by Picea sp. populations, which were associated with Populus sp. and Larix laricina, followed by progressive encroachment by Abies balsamea and Betula papyrifera. The decrease in green alder pollen, which shows maximum representation during the afforestation phase, indicates the closure of the forest canopy. The afforestation phase ended around 9000 years BP on the plateau but the timing of events was slightly different in the valley. The heliophilous plants persisted there, possibly due to active slope dynamics. The balsam firwhite birch community occupied the plateau since 9000 years BP with only small fluctuations in the relative abundance of the tree species. On the other hand, important changes took place in the valley until 5000 to 4000 years BP, when the successive immigration of Betula alleghaniensis, Pinus strobus, Fraxinus nigra, Acer saccharum and Ulmus americana occurred. This development initiated the present vegetational complex. This study clearly demonstrates that the sugar maple communities never colonized the plateau and occurred in the valley only since the Upper Holocene. This is in contradiction with Dansereau's hypothesis (1944) where the sugar maple communities in the Gaspé Peninsula are interpreted as relict stands of a previously widespread distribution of Acer saccharum during the climatic optimum of the Holocene. The late immigration of sugar maple in the area appears to be mostly due to topo-climatic barriers creating discontinuities in the habitats suitable for the species.Die Pollen-Analysen und die makrofossilen Analysen der Sedimente zweier Seen in der Umgebung des Mont-Saint-Pierre (Gaspésie), wovon einer im Kustental, der andere auf der Hochebene gelegen ist, ermôglichen die postglaziale Geschichte der Vegetation in zwei geomorphologisch kontrastiven Gebieten zu rekonstruieren. Nur die Hochebene war von einer ersten Vegetation vom Typus der Tundra (> 10 400 Jahre v.u.Z.) bewachsen, wàhrend das TaI noch zum Teil vom Goldthwait-Meer uberschwemmt war. Die Bewaldung der Hochebene war zuerst durch Picea sp. Bestànde charakterisiert, gefolgt von Populus sp. und Larix laricina, und dann durch ein progressives Uberhandnehmen von Abies balsamea und von Betula papyrifera. DasZuruckgehendes Pollen-Vorkommens der grunen Erie (Alnus cf. crispa), welche in der Bewaldungsphase ihr Hôchstvorkommen erreicht hatte, scheint ein zuverlàssiger lndikator fur die SchlieBung der Walddecke zu sein. Dièse Phase endet gegen 9000 Jahre v.u.Z. auf der Hochebene. Im TaI war der Rhythmus der Bewaldung anders. Heliophile Pflanzen konnten sich dort langer halten, was in Verbindung zur Aktivitàt der Steilabhânge, die das TaI sâumen, gebracht werden kann. Trotz der Variationen in der relativen Dichte der Baume hat der Tannenwald mit WeiRbirken zweifellos die Hochebene seit etwa 9000 Jahren v.u.Z. bedeckt. Hingegen hat sich die Vegetation des Tais ziemlich verândert bis gegen 5000 bis 4500 Jahren v.u.Z. durch die sukzessive Wanderung von Betula alleghaniensis, Pinus strobus, Fraxinus nigra, Acer saccharum und Ulmus americana. Die allmàhliche Ansiedlung dieser relativ wàrmeliebenden Baume ist der Grund fur die Vielfalt der heutigen Landschaft des TaIs. Die Daten zeigen, daB diese Ahornwâlder aus dem spâten Holozan stammen, wobei das Wandern von Acer saccharum zweifellos druch ortliche klimatische Schranken gebremst wurde, die zu einer deutlichen Diskontinuitât der Gebiete, die sich fur die Aufnahme dieser Art eignen, gefuhrt hat

Digital Doppler extraction demonstration with the advanced receiver

A digital Doppler extraction demonstration with the Advanced Receiver 2 (ARX 2) tracking Pioneer 10 and Voyager 2 is described. The measured results are compared with those of the Block 4 receiver that was operating in parallel with the ARX 2. It is shown that the ARX 2 outperforms the Block 4 receiver in terms of Allan variance of the Doppler residuals, the amount of which depends on the scenario of interest

Statistics of Auroral Langmuir Waves

The Physics of Auroral Zone Electrons II (PHAZE II) sounding rocket was launched in February 1997 into active pre-midnight aurora. The resulting high frequency wave data are dominated by Langmuir waves. Consistent with many previous observations the Langmuir waves are sporadic, occurring in bursts lasting up to a few hundred ms. We compute statistics of the electric field amplitudes of these Langmuir waves, with two results. First, the shape of the distribution of running averages of the electric field amplitudes remains approximately stationary for a large range of widths of running average less than ~0.3 ms and for a large range of widths exceeding about 1 ms. The interpretation of this transition timescale is unclear but appears unlikely to be of instrumental origin. Second, for 2.6-ms running averages, corresponding to the latter range, the distribution of the logarithm of electric field amplitudes matches a Gaussian form very well for all nine cases studied in detail, hence the statistics are lognormal. These distributions are consistent with stochastic growth theory (SGT)

Details on the O(meα6){\cal{O}}(m_e \alpha^6) Positronium Hyperfine Splitting due to Single Photon Annihilation

A detailed presentation is given of the analytic calculation of the single-photon annihilation contributions to the positronium ground state hyperfine splitting to order $m_e\alpha^6$ in the framework of non-relativistic effective theories. The current status of the theoretical description of the positronium ground state hyperfine splitting is reviewed.Comment: 27 pages, latex, 5 postscript figures; typos correcte

Right-Hand Polarized 4\u3ci\u3ef\u3c/i\u3e\u3csub\u3ece\u3c/sub\u3e Auroral Roar Emissions: 2. Nonlinear Generation Theory

Auroral roar emissions are commonly interpreted as Z (or upper hybrid) mode naturally excited by precipitating auroral electrons. Subsequent conversion to escaping radiation makes it possible for these emissions to be detected on the ground. Most emissions are detected as having left-hand (L) circular (or ordinary O) polarization, but the companion paper presents a systematic experimental study on the rare occurrence of the right-hand polarized, or equivalently, extraordinary (X) mode 4fce emission. A similar observation was reported earlier by Sato et al. (2015). The suggested emission mechanism is the nonlinear coalescence of two upper hybrid roars at 2fce. The present paper formulates a detailed theory for such an emission mechanism

Treating Homeless Opioid Dependent Patients with Buprenorphine in an Office-Based Setting

CONTEXT Although office-based opioid treatment with buprenorphine (OBOT-B) has been successfully implemented in primary care settings in the US, its use has not been reported in homeless patients. OBJECTIVE To characterize the feasibility of OBOT-B in homeless relative to housed patients. DESIGN A retrospective record review examining treatment failure, drug use, utilization of substance abuse treatment services, and intensity of clinical support by a nurse care manager (NCM) among homeless and housed patients in an OBOT-B program between August 2003 and October 2004. Treatment failure was defined as elopement before completing medication induction, discharge after medication induction due to ongoing drug use with concurrent nonadherence with intensified treatment, or discharge due to disruptive behavior. RESULTS Of 44 homeless and 41 housed patients enrolled over 12 months, homeless patients were more likely to be older, nonwhite, unemployed, infected with HIV and hepatitis C, and report a psychiatric illness. Homeless patients had fewer social supports and more chronic substance abuse histories with a 3- to 6-fold greater number of years of drug use, number of detoxification attempts and percentage with a history of methadone maintenance treatment. The proportion of subjects with treatment failure for the homeless (21%) and housed (22%) did not differ (P=.94). At 12 months, both groups had similar proportions with illicit opioid use [Odds ratio (OR), 0.9 (95% CI, 0.5–1.7) P=.8], utilization of counseling (homeless, 46%; housed, 49%; P=.95), and participation in mutual-help groups (homeless, 25%; housed, 29%; P=.96). At 12 months, 36% of the homeless group was no longer homeless. During the first month of treatment, homeless patients required more clinical support from the NCM than housed patients. CONCLUSIONS Despite homeless opioid dependent patients' social instability, greater comorbidities, and more chronic drug use, office-based opioid treatment with buprenorphine was effectively implemented in this population comparable to outcomes in housed patients with respect to treatment failure, illicit opioid use, and utilization of substance abuse treatment

A Model of Zebra Emission in Solar Type IV Radio Bursts

Solar type IV radio bursts present a theoretical challenge because they are composed of both continuum emission and fine structures. The latter include zebra bursts, which appear as harmonically spaced multiplets that shift in frequency with time. Similarities between these features and terrestrial auroral emissions suggest a new model to explain zebra-structured type IV emissions. In this model, the basic generation mechanism is identical with that proposed by Winglee and Dulk: mode conversion of Z-mode waves generated by the cyclotron maser mechanism under the condition fuh = Nfce, with N an integer; however, we propose a twist on this model whereby the zebra bursts do not arise from multiple N-values. Rather, the presence of localized density irregularities within the type IV source region leads to trapping of the upper hybrid Z-mode waves in density enhancements, which results in a discrete spectrum of upper hybrid modes with nearly constant frequency spacing. The number m of quasi-harmonics is limited by the trapping (quantization) conditions. The problem is described by an equivalent Schrödinger equation for the trapped mode, which is solved for an (idealized) cylindrical square density irregularity. In this model, the eigenfrequency spacing matches the observed type IV frequency spacings for less than 10% density enhancements with individual scale sizes of 30-1000 thermal electron gyroradii, corresponding to 1-100 m scales in coronal loops. To produce the observed emitted power for a reasonable (\u3c1%) efficiency requires a large number of such individual microscopic sources occurring over a portion of a magnetic type IV loop at a restricted altitude within which the magnetic field and density are approximately constant. The loop plasma in the zebra emission source is thus highly turbulent in the sense that it contains a large number of density fluctuations. In this case transition radiation can effectively contribute to the radiation background and may also provide the wave power required in the upper hybrid range for generating zebra emissions

A note on the third family of N=2 supersymmetric KdV hierarchies

We propose a hamiltonian formulation of the $N=2$ supersymmetric KP type hierarchy recently studied by Krivonos and Sorin. We obtain a quadratic hamiltonian structure which allows for several reductions of the KP type hierarchy. In particular, the third family of $N=2$ KdV hierarchies is recovered. We also give an easy construction of Wronskian solutions of the KP and KdV type equations