From decimeter-scale elevated ionic conductivity regions in the cloud to lightning initiation.

In this work, we represent the lightning initiation scenario as a sequence of two transitions of discharge activity to progressively larger spatial scales: the first one is from small-scale avalanches to intermediate-scale streamers; and the second one is from streamers to the lightning seed. We postulate the existence of ion production centers in the cloud, whose occurrence is caused by electric field bursts accompanying hydrometeor collisions (or near collisions) in the turbulent thundercloud environment. When a new ion production center is created inside (fully or partially) the residual ion spot left behind by a previously established center, there is a cumulative effect in the increasing of ion concentration. As a result, the essentially non-conducting thundercloud becomes seeded by elevated ion-conductivity regions (EICRs) with spatial extent of 0.1-1 m and a lifetime of 1-10 s. The electric field on the surface of an EICR (due to its conductivity being at least 4 orders of magnitude higher than ambient) is a factor of 3 or more higher than ambient. For a maximum ambient electric field of 100 kV/m typically measured in thunderclouds, such field enhancement is sufficient for initiation of positive streamers and their propagation over distances of the order of decimeters, and this will be happening naturally, without any external agents (e.g., superenergetic cosmic ray particles) or extraordinary in-cloud conditions, such as very high potential differences or very large hydrometeors. Provided that each EICR generates at least one streamer during its lifetime, the streamers will form a 3D network, some parts of which will contain hot channel segments created via the cumulative heating and/or thermal-ionizational instability. These hot channel segments will polarize, interact with each other, and cluster, forming longer conducting structures in the cloud. When the ambient potential difference bridged by such a conducting structure exceeds 3 MV, we assume that the lightning seed, capable of self-sustained bidirectional extension, is formed.

A study of the ground-attachment process in natural lightning with emphasis on its breakthrough phase.

Synchronized high-speed (124 or 210 kiloframes per second) video images and wideband electromagnetic field records of the attachment process were obtained for 4 negative strokes in natural lightning at the Lightning Observatory in Gainesville, Florida. The majority of imaged upward connecting leaders (UCLs) and upward unconnected leaders, inferred to be mostly initiated from trees, exhibited a pulsating behavior (brightening/fading cycles). UCLs, whose maximum extent ranged from 11 to 25 m, propagated in virgin air at speeds ranging from 1.8 × 105 to 6.0 × 105 m/s with a mean of 3.4 × 105 m/s. Within about 100 m of the ground, the ratio of speeds of the downward negative leader and the corresponding positive UCL was about 3-4 for 2 events and 0.5 for 1 event. The breakthrough phase (final jump) was imaged for 2 events. The initial length of the common streamer zone (CSZ) was estimated to be about 30-40 m. For 2 events, speeds of positive and negative leaders developing toward each other inside the CSZ were found to be between 2.4 × 106 and 3.7 × 106 m/s. For 1 event, opposite polarity leaders were observed to accelerate inside the CSZ. The current at the end of the breakthrough phase, lasting on average 4.7 µs, was estimated to be approximately one-half of the overall current peak. Thus, about one-half of the current peak traditionally attributed to the return-stroke process is actually associated with two leaders extending toward each other to collision inside the CSZ.

Initiation and propagation of cloud-to-ground lightning observed with a high-speed video camera.

Complete evolution of a lightning discharge, from its initiation at an altitude of about 4 km to its ground attachment, was optically observed for the first time at the Lightning Observatory in Gainesville, Florida. The discharge developed during the late stage of a cloud flash and was initiated in a decayed branch of the latter. The initial channel section was intermittently illuminated for over 100 ms, until a bidirectionally extending channel (leader) was formed. During the bidirectional leader extension, the negative end exhibited optical and radio-frequency electromagnetic features expected for negative cloud-to-ground strokes developing in virgin air, while the positive end most of the time appeared to be inactive or showed intermittent channel luminosity enhancements. The development of positive end involved an abrupt creation of a 1-km long, relatively straight branch with a streamer corona burst at its far end. This 1-km jump appeared to occur in virgin air at a remarkably high effective speed of the order of 106 m/s. The positive end of the bidirectional leader connected to another bidirectional leader to form a larger bidirectional leader, whose negative end attached to the ground and produced a 36-kA return stroke.

Ultra-low-dose continuous combined estradiol and norethisterone acetate: improved bleeding profile in postmenopausal women.

OBJECTIVE: To evaluate the effect of two ultra-low-dose hormone treatments containing estradiol (E2) 0.5 mg and norethisterone acetate (NETA) 0.1 or 0.25 mg on the endometrium and bleeding. METHODS: A prospective, randomized, placebo-controlled trial of 6 months. Local Ethics Committee approval and informed consent were obtained prior to initiation and enrollment. Out of 577 postmenopausal women randomized, 575 took E2/NETA 0.1 (n = 194), or E2/NETA 0.25 (n = 181) or placebo (n = 200). Endometrial bleeding was monitored by daily diary cards and endometrial thickness by transvaginal ultrasound at baseline and on completion. An endometrial biopsy was obtained when indicated clinically. RESULTS: In months 1-6, the amenorrhea rates with E2/NETA 0.1 were 89%, 89%, 86%, 85%, 89% and 89%, respectively and the no-bleeding rates were correspondingly high: 95%, 94%, 93%, 90%, 95% and 95%. The amenorrhea and spotting-only rates were similar with both ultra-low-dose combinations. The withdrawal rates due to bleeding were very low and the same in all three treatment arms (n = 1; 1%). There was a slight increase in the mean endometrial thickness in all three groups, which remained less than 5 mm. CONCLUSIONS: The ultra-low-dose combination of E2/NETA 0.1 or E2/NETA 0.25 resulted in a high incidence of amenorrhea and no bleeding in postmenopausal women, and a corresponding high level of compliance. Overall, there was no significant change in mean endometrial thickness during 6 months of active treatment or placebo.

Dose-dependent changes of the ratio of apoptosis to proliferation by norethisterone and medroxyprogesterone acetate in human breast epithelial cells.

OBJECTIVE: There is increasing evidence that adding progestogens to estrogen replacement therapy may do more harm than good; however, whether all progestogens act equally on breast cells is debatable. Apart from estrogens, mitogenic growth factors from stromal breast tissue are important in growth-regulation of breast cells, and may modify the response to progestogens. We investigated the effects of medroxyprogesterone acetate (MPA) as well as norethisterone (NET) in the presence of a growth factor mixture and/or estradiol in normal and cancerous human epithelial breast cells. METHODS: MCF10A cells (human epithelial, estrogen- and progesterone-receptor negative, normal breast cells), HCC1500 (human estrogen and progesterone receptor-positive primary breast cancer cells) and MCF-7 cells (human estrogen and progesterone receptor-positive metastatic breast cancer cell line) were used in the experiments. The cells were incubated with progestogens at concentrations of 10(-10) to 10(-6) M for 7 days and growth factors (GFs), estradiol (E2) alone and a combination of GFs + E2. Cell proliferation rate was measured by ATP assay. Apoptosis was measured by cell death assay. Ratios of cell death : proliferation were calculated from these results. RESULTS: In MCF10A cells growth factors elicited a decrease in the ratio of apoptosis to proliferation. This effect was further stimulated by the addition of MPA, whereas NET had no effect. In HCC cells growth factors and estradiol alone and in combination led to a reduction in the ratio. This effect could be partly reversed dose-dependently by the addition of MPA and NET, being more pronounced for MPA. Similar results were found for MCF-7 cells stimulated by estradiol. CONCLUSION: The results of our investigations demonstrate that there are differences between the two progestogens NET and MPA investigated with respect to their effects on normal and cancerous cells. By increasing the mitotic rate of normal epithelial cells, MPA may increase breast cancer risk in women when used in long-term treatment. In this respect NET reacts neutral. The mitosis of pre-existing cancerous cells may be partly inhibited by the addition of both progestogens. Thus, our results indicate that it is necessary to differentiate between normal and malignant breast cells concerning the assessment of progestogens as a risk factor for breast carcinogenesis.

Establishing low-energy sequential decomposition pathways of leucine enkephalin and its N- and C-terminus fragments using multiple-resonance CID in quadrupolar ion guide.

The simultaneous resonant low-energy excitation of leucine enkephalin and its fragment ions was demonstrated in a collision cell of the multipole-quadrupole time-of-flight instrument. Using low-amplitude multiple-resonance excitation CID, we were able to show the exclusive sequential fragmentation of N- and C-terminus fragments all the way to the final fragments--immonium ions of phenylalanine or tyrosine. In this CID mode the single-channel dissociation of each new generation of fragments followed the lowest energy decomposition pathways observable on the time scale of our experiment. Up to six generations of sequential dissociation were carried out in multiple-resonance CID experiments. The direct qualitative comparison of fragmentation of axial-acceleration versus resonant (radial) CID was performed in the same instrument. In both activation methods, fragmentation patterns suggested complex decomposition mechanisms attributable to dynamic competition between sequential and parallel dissociation channels.

Excitation of ions by high-harmonic frequency components in Paul and Penning traps and ion guides. I. Selective simultaneous dipolar excitation of high charge states with clipped sinusoidal and non-harmonic waveforms in a linear quadrupole ion guide.

This article presents a method for simultaneous excitation of multiple high charge states of a molecular ion in Paul or Penning trap. Using a linear quadrupolar ion guide we validate the method by using a variety of time- domain excitation waveforms with high harmonics of the first charge state's resonant frequency. The proposed way of inducing harmonics is the deliberate distortion of the excitation waveform from its sinusoidal form. In order to facilitate interference of the harmonics, a superposition of two sinusoids different by a frequency factor of two is used. The simplest form of distortion - amplitude restriction - of such waveform produces interference of the harmonics and results in selective excitation of charge states. Multiple protonation states of melittin were used as a model in this study.

[Amenorrhea rate after switch from sequential hormone replacement therapy to continuous combined administration of low dose estradiol and norethisterone acetate]. / Blutungsfreiheit nach der Umstellung von einer sequenziellen Hormonersatztherapie auf die kontinuierlich kombinierte Gabe von niedrig dosiertem Estradiol und Norethisteronacetat.

OBJECTIVE: Patient's wishes for a hormone replacement therapy (HRT) without withdrawal bleedings are decisive for a good compliance. Systematic experience concerning the bleeding profile when switching from a sequential hormone replacement therapy (s.c.HRT) to a continuous combined hormone replacement therapy (c.c.HRT) is sparse. This non-interfering study is designed to investigate the bleeding profile after such a switch. MATERIAL AND METHODS: 1 018 gynaecological centres recruited 3 917 patients pretreated with a s.c.HRT for this study. The switch from the s.c.HRT to the c.c.HRT was performed with a low-dose combination of 1 mg estradiol plus 0.5 mg norethisterone acetate (NETA). The bleeding profile was evaluated after 6 to 9 months of treatment according to the patient's diaries. RESULTS: Amenorrhoea was reached in 74.4 % of the enrolled patients after 3 months, in 90.6 % after 6 months, and in 92.1 % after 9 months of treatment. At the time of the switch to the c.c.HRT, already 32.4 % of the women were free of withdrawal bleedings. Parameters like age of the patients, body mass index (BMI), dosage of the estrogen during pretreatment did not influence the results considerably. 92.7 % of the physicians and 92.5 % of the women rated the combined treatment of 1 mg estradiol and 0.5 mg NETA (Activelle) as satisfactory. CONCLUSION: The switch from a s.c.HRT to a continuous combined treatment with 1 mg estradiol plus 0.5 mg NETA can be performed without problems, resulting in a high rate of amenorrhoea and a high acceptance of physicians as well as patients.

Low-energy collision-induced dissociation fragmentation analysis of cysteinyl-modified peptides.

The development of methods to chemically modify and isolate cysteinyl-residue-containing peptides (Cys-peptides) for LC-MS/MS analysis has generated considerable interest in the field of proteomics. Methods using isotope-coded affinity tags (ICAT) and (+)-biotinyl-iodoacetamidyl-3,6-dioxaoctanediamine (iodoacetyl-PEO-biotin) employ similar Cys-modifying reagents that contain a thiolate-specific biotin group to modify and isolate Cys-containing peptides in conjunction with immobilized avidin. For these strategies to be effective on a proteome-wide level, the presence of the ICAT or acetyl-PEO-biotin tag should not interfere with the efficiency of induced dissociation in MS/MS experiments or with the identification of the modified Cys-peptides by automated database searching algorithms. We have compared the collision-induced dissociation (CID) fragmentation patterns of peptides labeled with iodoacetyl-PEO-biotin and the ICAT reagent to those of the unmodified peptides. CID of Cys-peptides modified with either reagent resulted in the formation of ions attributed to the modified Cys-peptides as well as those unique to the labeling reagent. As demonstrated by analyzing acetyl-PEO-biotin labeled peptides from ribonuclease A and the ICAT-labeled proteome of Deinococcus radiodurans, the presence of these label-specific product ions provides a useful identifier to discern whether a peptide has been modified with the Cys-specific reagent, especially when a number of peptides analyzed using these methods do not contain a modified Cys residue, and to differentiate identical Cys-peptides labeled with either ICAT-d0 or ICAT-d8.