Near-surface ocean current sensors : problems and performance

When current meters are used to measure mean horizontal currents in surface gravity waves, immunity to the vertical component of flow is important, even though the net vertical flow averages to zero and is normal to the desired horizontal components. A technique is presented for estimating the magnitude of the errors introduced by imperfect rejection of the off-axis flows (cross-talk) from laboratory measurements of the current meter "vertical-cosine-response." The predicted dynamic response is shown to compare favorably with laboratory measurements. The measured steady state vertical-cosine-response functions for several practical current sensors are summarized and used to estimate the magnitude of wave-induced errors in horizontal mean current measurements. A new dye technique for evaluating near-surface current meter performance in waves is shown.Prepared for the Working Con6enence on CURRENT MEASUREMENTS sponsored by the NOAA 0ffice of Ocean Engineering with the Delaware Sea Grant College Program

Moored acoustic travel time (ATT) current meters : evolution, performance, and future designs

New laboratory measurements and numeric model studies show the present folded-path ATT current meters are stable and sensitive, but are not well suited for mean flow observations in surface gravity waves. Alternate designs which reduce unwanted wake effects are proposed. ATT flowmeter history, principles of acoustic flow sensors, mean flow near cylinders, and the need for linear flow sensors are reviewed.Prepared for the Office of Naval Research under Contract Number N00014-76-C-0197; NR083-400 to the Woods Hole Oceanographic Institution

Summary of current meter operations in 1968

Originally issued as Reference No. 69-14, series later renamed WHOI-This report describes work done with Geodyne current meters and wind recorders during 1968. Techniques for testing instruments prior to use at sea, instrument performance at sea and instrument changes evolved during the year are discussed.Submitted to the Office of Naval Research under ContractN00014-66-C0241, NR 083-004

Vector averaging current meter speed calibration and recording technique

Equations 1-4 summarize the rotor calibration used at Woods Hole Oceanographic Institution for the VACM. A discussion of the instrumental and test details used to derive these equations follows. A list of other VACM documents and related bibliography is included.Prepared for the Office of Naval Research under Contract N00014-66-C0241; NR 083-004; N00014- 74-C0262; NR 083-004; and IDOE/NSF Grant GX-29054

Loran-C Latitude-Longitude Conversion at Sea : Programming Considerations

To aid programmers of Loran-C latitude-longitude conversion, we : 1. Provide reference to the literature. 2. Compare digital “processings-noise” for several arc-length methods. 3. Discuss some practical aspects of overland signal propagation (ASF) modeling for offshore navigation. Comparisons are made of the precision of arc-length routines as computer precision is reduced. Overland propagation delays (ASF's) are discussed and illustrated with observations from offshore New England. Present practice of Loran-C error budget modeling is then reviewed with the suggestion that additional terms be considered in future modeling

Cytoplasmic BK\u3csub\u3eCa\u3c/sub\u3e channel intron-containing mRNAs contribute to the intrinsic excitability of hippocampal neurons

High single-channel conductance K+ channels, which respond jointly to membrane depolarization and micromolar concentrations of intracellular Ca2+ ions, arise from extensive cell-specific alternative splicing of pore-forming α-subunit mRNAs. Here, we report the discovery of an endogenous BKCa channel α-subunit intron-containing mRNA in the cytoplasm of hippocampal neurons. This partially processed mRNA, which comprises ≈10% of the total BKCa channel α-subunit mRNAs, is distributed in a gradient throughout the somatodendritic space. We selectively reduced endogenous cytoplasmic levels of this intron-containing transcript by RNA interference without altering levels of the mature splice forms of the BKCa channel mRNAs. In doing so, we could demonstrate that changes in a unique BKCa channel α-subunit introncontaining splice variant mRNA can greatly impact the distribution of the BKCa channel protein to dendritic spines and intrinsic firing properties of hippocampal neurons. These data suggest a new regulatory mechanism for modulating the membrane properties and ion channel gradients of hippocampal neurons

Solitonic supersymmetry restoration

Q-balls are a possible feature of any model with a conserved, global U(1) symmetry and no massless, charged scalars. It is shown that for a broad class of models of metastable supersymmetry breaking they are extremely influential on the vacuum lifetime and make seemingly viable vacua catastrophically short lived. A net charge asymmetry is not required as there is often a significant range of parameter space where statistical fluctuations alone are sufficient. This effect is examined for two supersymmetry breaking scenarios. It is found that models of minimal gauge mediation (which necessarily have a messenger number U(1)) undergo a rapid, supersymmetry restoring phase transition unless the messenger mass is greater than 10^8 GeV. Similarly the ISS model, in the context of direct mediation, quickly decays unless the perturbative superpotential coupling is greater than the Standard Model gauge couplings.Comment: 17 pages, 3 figures, minor comments added, accepted for publication in JHE

Detection of 6 November 1997 ground level event by Milagrito

Solar Energetic Particles (SEPs) with energies exceeding 10 GeV associated with the 6 November 1997 solar flare/CME (coronal mass ejection) have been detected with Milagrito, a prototype of the Milagro Gamma Ray Observatory. While SEP acceleration beyond 1 GeV is well established, few data exist for protons or ions beyond 10 GeV. The Milagro observatory, a ground based water Cherenkov detector designed for observing very high energy gamma ray sources, can also be used to study the Sun. Milagrito, which operated for approximately one year in 1997/98, was sensitive to solar proton and neutron fluxes above ∼4 GeV. In its scaler mode, Milagrito registered a rate increase coincident with the 6 November 1997 ground level event observed by Climax and other neutron monitors. A preliminary analysis suggests the presence of \u3e10 GeV particles

First results of a study of TeV emission from GRBs in Milagrito

Milagrito, a detector sensitive to γ-rays at TeV energies, monitored the northern sky during the period February 1997 through May 1998. With a large field of view and high duty cycle, this instrument was used to perform a search for TeV counterparts to γ-ray bursts. Within the Milagrito field of view 54 γ-ray bursts at keV energies were observed by the Burst And Transient Satellite Experiment (BATSE) aboard the Compton Gamma-Ray Observatory. This paper describes the results of a preliminary analysis to search for TeV emission correlated with BATSE detected bursts. Milagrito detected an excess of events coincident both spatially and temporally with GRB 970417a, with chance probability 2.8×10−5 within the BATSE error radius. No other significant correlations were detected. Since 54 bursts were examined the chance probability of observing an excess with this significance in any of these bursts is 1.5×10−3. The statistical aspects and physical implications of this result are discussed

Milagro: A TeV observatory for gamma-ray bursts

Observation of prompt TeV γ-rays from GRBs requires a new type of detector to overcome the low duty factor and small field of view of current TeV observatories. Milagro is such a new type of very high energy (\u3e a few 100 GeV) gamma-ray observatory, which has a large field of view of \u3e1 steradian and 24 hours/day operation. Milagrito, a prototype for Milagro, was operated from February 1997 to May 1998. During the summer of 1998, Milagrito was dismantled and Milagro was built. Both detectors use a 80 m×60 m×8 m pond of water in which a 3 m×3 m grid of photomultiplier tubes detects the Cherenkov light produced in the water by the relativistic particles in extensive air showers. Milagrito was smaller and had only one layer of photomultipliers, but allowed the technique to be tested. Milagrito observations of the Moon’s shadow and Mrk 501 are consistent with the Monte Carlo prediction of the telescope’s parameters, such as effective area and angular resolution. Milagro will have improved flux sensitivity over Milagrito due to larger effective area, better angular resolution and cosmic-ray background rejection