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In order to study the Mn nutrition of bidi tobacco plant ( Nicotiana tabacum L. aromatic strain 2-1) when it is supplied with nutrient solutions containing different ratios of Mn with Fe, P, K and Ca, a sand-culture experiment was carried out in four different series viz. Fe-Mn, K-Mn, P-Mn and Ca-Mn. No characteristic deficiency symptoms except general loss of green colour and diminished growth were observed at 0.1 ppm Mn in the nutrient solution. Toxicity was observed when Mn in the nutrient solution was 100 ppm and severity of the symptoms decreased with increase in Fe-Mn or K-Mn ratios, but it increased when P-Mn ratio increased while in Ca-Mn series it first decreased and then increased at still higher concentration of Ca on account of chloride ion effect as CaCl had to be added to bring about 500 ppm concentration of Ca necessary for the treatment. No symptoms of deficiency or toxicity were observed when Mn in nutrient solution varied from 1 to 10 ppm and Fe-Mn ratio for the leaf varied from 0.4 to 6.1 and its Mn content varied from 190 to 1575 ppm. Slight loss of green colour and plant vigour appeared when Fe-Mn ratio for the leaf was higher than 12.8 even though the Mn content was as high as 90 ppm. Toxic effect due to excessive Mn was felt when Fe-Mn ratio was 0.35 or less and leaf content 1875 ppm or more. Nicotine content was inversely related to the intensity of Mn-toxicity. [ABSTRACT FROM AUTHOR]

The previously observed negative resistance in double heterostructure diodes is shown to be caused by a trap generated potential barrier near the heterojunction nGaAlAs− pGaAs. The filling and emplying times were measured by observing the breakdown of the barrier with single and double pulses. Time resolved spectral measurements confirm the model. [ABSTRACT FROM AUTHOR]